Relationship between IgM deposition intensity in renal tissue and 5-year renal prognosis in immunoglobulin A nephropathy

doi:10.21203/rs.3.rs-4898300/v1

[Objective] This study aimed to examine both the clinical and renal tissue humoral immunodeposition profiles in immunoglobulin A nephropathy (IgAN) and identify factors influencing its prognosis. [Methods] A retrospective analysis was conducted on clinicopathological data from 774 patients with primary IgAN, confirmed via renal biopsy, at Hangzhou Hospital of Traditional Chinese Medicine between January 1, 2016, and December 31, 2018. Patients were categorized into end-event and non-end-event groups based on whether they reached the renal composite endpoint, defined as a ≥ 50% decline in eGFR or progression to end-stage renal disease (ESRD). Risk factors for adverse renal outcomes were evaluated using univariate and multivariate Cox regression models. Patients were further divided into three groups based on IgM deposition levels in the glomerular mesangial area: IgM-negative, low (IF ≤ 2+), and high (IF > 2+). Comparative analyses of clinical and histopathological characteristics, along with treatment regimens, were performed across these groups. [Results] The high IgM deposition group exhibited significantly lower serum albumin and eGFR levels, alongside higher cholesterol, 24-hour urine protein, and blood immunoglobulin M levels compared to the IgM-negative and low deposition groups. Multivariate Cox regression analysis identified immunosuppressant use as an independent protective factor for IgAN prognosis, while low serum albumin, T2 lesions, and nephropathological IgM deposits were recognized as independent risk factors for the 5-year prognosis of IgAN. Kaplan-Meier survival curves revealed that patients with high IgM deposition had markedly poorer prognoses compared to those with negative or low deposition. [Conclusion] Besides low serum albumin and T2 lesions, IgM deposition in the mesangial region emerged as an independent risk factor for the 5-year prognosis of IgAN.

IgA nephropathy

prognosis

renal biopsy

IgM deposition

Immunoglobulin A nephropathy (IgAN) represents the most prevalent primary glomerular disease and a leading cause of end-stage renal disease (ESRD). Typically, immunofluorescence reveals IgA deposition in the mesangial region, occasionally extending to capillary loops, often accompanied by C3 deposition but rarely C1q. IgG and IgM deposits may also be present, mirroring the distribution of IgA but with reduced intensity^[1]. Managing IgAN is challenging due to its diverse clinical and pathological manifestations and the variability in therapeutic responses and prognoses^[2]. Prior research has identified several risk factors for poor renal outcomes in patients with IgAN^[3][4], such as hypertension, reduced estimated glomerular filtration rate (eGFR), and proteinuria. The Oxford Typing Score (MEST-C) has recently been validated as a tool for assessing pathological lesions in IgAN^[5], showing a strong correlation with clinical presentation and prognosis. Moreover, emerging evidence highlights the significant role of humoral immunity activation in the inflammatory cascade and tissue damage associated with IgAN^[6][7]. However, the prognostic value of humoral immune indicators, including renal IgM, IgG, C1q, and C3 deposition, remains unclear. This study retrospectively examined clinical and renal tissue humoral immune deposition data from patients with IgAN at Hangzhou Hospital of Traditional Chinese Medicine (2016–2018), aiming to identify novel risk factors for the 5-year prognosis of IgAN and provide clinical guidance.

1 Research object

Patients diagnosed with IgAN via renal biopsy at Hangzhou Hospital of Traditional Chinese Medicine between January 1, 2016, and December 31, 2018, were included in this study (n = 894). The inclusion criteria were: (1) complete case data; (2) follow-up duration of at least 6 months; (3) age between 18 and 75 years. Exclusion criteria encompassed: (1) secondary IgAN, including purpura nephritis, hepatitis B virus-associated nephritis, lupus nephritis, and diabetic nephropathy; (2) acute kidney injury; (3) ESRD at the time of biopsy; (4) follow-up less than 6 months or no composite endpoint event within 6 months; (5) missing baseline data. Approved by the Ethics Committee of Hangzhou Hospital of Traditional Chinese Medicine, this retrospective study exempted participants from signing informed consent (ethics number: 2021KY045).

2 Clinical and laboratory data

Clinical and laboratory data at the time of renal biopsy were extracted from the hospital’s medical record system and included biopsy date, sex, age, systolic blood pressure (SBP), diastolic blood pressure (DBP), body mass index (BMI), hemoglobin (HB), serum albumin (Alb), cholesterol (TC), triglycerides (TG), low-density lipoprotein (LDL), high-density lipoprotein (HDL), blood uric acid (UA), serum creatinine (Scr), 24-hour urine total protein (24h-UTP), microscopic examination of red blood cells, estimated glomerular filtration rate (eGFR), and serum humoral immune indicators (IgA, IgG, IgM, C3, C4). Hypertension was defined as three measurements of SBP ≥ 140 mmHg and/or DBP ≥ 90 mmHg on different dates and/or a history of hypertension. eGFR was calculated using the CKD Epidemiology Collaboration (CKD-EPI) creatinine equation, with all indicators assessed according to traditional cut-off values per KDIGO guidelines^[8].

3 Histopathological data

Histopathological data were obtained from the Department of Nephrology at Hangzhou Hospital of Traditional Chinese Medicine. Kidney biopsy tissues were subjected to routine staining procedures including HE, PAS, silver hexamide, and Masson's staining. Direct immunofluorescence was employed to detect the expression intensity and localization of IgA, IgG, IgM, C3, C4, and C1q. Pathological indicators were scored for each patient, including the Oxford IgA scale (MEST-C score) to describe tissue lesions: M (mesangial cell proliferation), E (increased capillary cells), S (segmental sclerosis), T (tubular atrophy or interstitial fibrosis), and C (crescent formation). Mesangial lesions were classified as M0 or M1 based on cell proliferation. E and S lesions were categorized as E0/E1 and S0/S1, depending on their presence. Crescent bodies were defined as extrinsic capillary proliferation exceeding two cell layers of any size. Tubular/stromal and crescent lesions were graded as T0 (0-25%), T1 (26-50%), or T2 (> 50%), and C0 (none), C1 (0-25%), or C2 (≥ 25%), respectively. All biopsy specimens were reviewed by two renal pathologists who were blinded to clinical data. The anti-IgM antibody used was a polyclonal rabbit anti-human secondary antibody (F0203) from Agjlent Dako (Copenhagen, Denmark), diluted 1:50. Immunofluorescence sections were reported with a positivity scale from 0 to 4+: (-) not visible at any magnification; (±) faintly visible under high power; (+) visible under high power and faintly under low power; (++) clearly visible under high power and visible under low power; (+++) dazzling under high power and clearly visible under low power; (++++) dazzling at both high and low power. Patients were categorized into three groups based on IgM deposition in the glomerular mesangial area: IgM-negative, low (IF ≤ 2+), and high (IF > 2+). Clinical and histopathological characteristics, as well as treatments, were compared among these groups^[9].

4 Treatment, endpoints, and follow-up

The study documented the use of glucocorticoids, immunosuppressants, or renin-angiotensin system (RAS) blockers throughout the disease course. A composite endpoint was defined as either end-stage renal disease (eGFR < 15 mL/min/1.73 m² or dialysis) or a permanent eGFR decline of ≥ 50%^[10]. At each follow-up visit within 5 years of the renal biopsy, data on serum creatinine (SCr), eGFR, total follow-up duration, and the occurrence of the renal composite endpoint were recorded. In cases where this information was missing, telephone inquiries were made.

5 Statistical Analysis

Data analysis was performed using Statistical Package for Social Sciences (SPSS) version 26.0 (IBM, Chicago, IL, USA), and graphs were created with GraphPad Prism version 9.5.1 (GraphPad Software, San Diego, CA, USA). The Kolmogorov-Smirnov test assessed the normality of measurement data, while the Levene test evaluated variance homogeneity. Normally distributed data were reported as mean ± standard deviation (x( _ ) ± s) and compared using the t-test. Non-normally distributed data were presented as M (P₂₅, P₇₅), with comparisons made using the Mann-Whitney U-test. Categorical variables were expressed as frequencies (percentages), with group comparisons performed using the X² test or Fisher's exact test, and rank data comparisons also made with the Mann-Whitney U test. Multivariate Cox regression analysis identified risk factors for complex outcomes in patients with IgAN. Kaplan-Meier survival curves analyzed cumulative renal survival. Statistical significance was set at P < 0.05 for all two-sided tests.

1 Clinical and pathological indices and treatment status of patients with IgAN exhibiting different outcomes over 5 years

The enrollment process is detailed in Fig. 1. A total of 774 patients with primary IgAN were ultimately included, comprising 306 males (39.5%) and 468 females (60.5%). Among these, 56 patients (7.2%) reached the renal composite endpoint. The patients were categorized into endpoint and non-endpoint groups based on the occurrence of endpoint events (Table 1). The median follow-up duration was 48 months (range: 34 to 60 months) for the non-endpoint group and 32 months (range: 10.5 to 52.5 months) for the endpoint group. No significant differences were observed between the two groups regarding body mass index (BMI), high-density lipoprotein (HDL), microscopic red blood cells, and levels of IgG, IgA, IgM, and complement C3 (P > 0.05). However, the endpoint group was older, had a higher proportion of males, and presented with significantly higher systolic and diastolic blood pressure, cholesterol, triglycerides, low-density lipoprotein (LDL), blood uric acid, serum creatinine, 24-hour urine protein, and complement C4 levels, alongside lower hemoglobin, serum albumin, and eGFR levels (P ≤ 0.05). Oxford classification (MEST-C score) revealed no significant difference in M scores between the two groups. The non-endpoint group exhibited more severe capillary cell proliferation, while the endpoint group had a higher prevalence of segmental sclerosis, renal tubular atrophy or interstitial fibrosis, and crescentic lesions. In terms of renal pathological immunofluorescence, the endpoint group demonstrated more pronounced IgM and C1q deposition, whereas the non-endpoint group had more severe C3 deposition. Therapeutic use comparisons in Table 1 indicated no significant difference in the administration of immunosuppressants and RAS blockers between the groups (P = 0.007 and P = 0.132, respectively), though the endpoint group received more glucocorticoids (P = 0.007).

Table 1

Clinical and histopathological features and treatment of renal biopsy in patients with IgAN exhibiting different outcomes over 5 years.Note: All data are expressed as frequency (percentage), mean ± standard deviation, or median (interquartile range). *P < 0.05 is considered statistically significant. Abbreviations: SBP: systolic blood pressure; DBP: diastolic blood pressure; BMI: body mass index; HB: hemoglobin; Alb: serum albumin; TC: cholesterol; TG: triglycerides; LDL: low-density lipoprotein; HDL: high-density lipoprotein; UA: blood uric acid; Scr: serum creatinine; UTP: 24-hour urine protein quantification; M: increased mesangial cells; E: increased intracellular cells in capillaries; T: renal tubular atrophy or interstitial fibrosis; C: crescent formation; RAS: renin-angiotensin system inhibitors; URBC: microscopic examination of red blood cells (0 is less than 3/HP, 1 is 4–9/HP, 2 is 10–30/HP, 3 is greater than 30/HP); eGFR: estimated glomerular filtration rate; IgA, IgG, IgM, C3, C4: blood and fluid immune indicators. The severity of immunofluorescence was rated as 1 (-+), 2 (+), 3 (++), 4 (+++), 5 (++++).
Variables	Non-endpoint event group (n = 718)	Endpoint event group (n = 56)	Total (n = 774)	P-value
Age (years)	36[29,45]	42.5[32,51.5]	36[29,46]	0.002*
Male, n(%)	277(38.6%)	29(51.8%)	306(39.5%)	0.052
Time (months)	48[34,60]	32[10.5,52.5]	48[31,60]	< 0.001*
BMI (kg/m²)	22.6[20.4,24.8]	23.0[19.4,25.9]	22.6[20.4,24.8]	0.768
SBP (mmHg)	121[111,131.5]	132.5[123,146]	122[111,134.3]	< 0.001*
DBP (mmHg)	77[68,85]	88[76,93.8]	77[68.6,86]	< 0.001*
HB (g/L)	121[111,133]	114[100,129]	120[110,133]	0.001*
Alb (g/L)	38.2[35.7,40.8]	34.5[29.2,38.4]	38[35.3,40.7]	< 0.001*
TC (mmol/L)	4.4[3.8,5.1]	5.1[4.4,5.9]	4.4[3.8,5.1]	< 0.001*
TG (mmol/L)	1.2[0.9,1.7]	1.6[1.3,2.2]	1.2[0.9,1.7]	< 0.001*
LDL (mmol/L)	2.6[2.2,3.1]	3.3[2.6,4.1]	2.7[2.2,3.2]	< 0.001*
HDL (mmol/L)	1.1[0.9,1.3]	1.1[0.9,1.3]	1.1[0.9,3.2]	0.889
UA (umol/L)	302[248,359]	350[295,433.5]	305[250,364]	< 0.001*
Scr (umol/L)	72[57,100]	134[108.3,196]	74.5[59,103]	< 0.001*
24h-UTP (g/day)	0.8[0.5,1.6]	2.7[1.8,3.9]	0.9[0.5,1.8]	< 0.001*
URBC	1[0,3]	1[0,3]	1[0,3]	0.582
eGFR (ml· min^− 1· 1.73m^− 2)	92[70,110.1]	42.5[30.2,58.9]	88.9[64.3,108.7]	< 0.001*
IgG (g/L)	1090[915,1270]	987[775,1300]	1090[907.3,1270]	0.091
IgA (g/L)	292[235,360]	276[240,347]	290.5[235,358.3]	0.398
IgM (g/L)	104[77.8,139]	116[78,148]	104[78,139]	0.304
C3 (g/L)	97[85,110]	94[87,110]	97[86,110]	0.958
C4 (g/L)	23[18,27]	26[21,31]	23[18,27]	0.003*
Optical microscope analysis
M, n(%)				1
0	6(0.8%)	0	6(0.8%)
1	712(99.2%)	56(100%)	768(99.2%)
E, n(%)				0.027*
0	503(70.1%)	47(83.9%)	550(71.1%)
1	215(29.9%)	9(16.1%)	224(28.9%)
S,n(%)				0.025*
0	120(16.7%)	3(5.4%)	123(15.9%)
1	598(83.3%)	53(94.6%)	651(84.1%)
T, n(%)				< 0.001*
0	559(77.9%)	9(16.1%)	559(72.2%)
1	181(25.2%)	24(42.9%)	181(23.4%)
2	34(4.7%)	23(41.1%)	34(4.4%)
C, n(%)				0.004*
0	251(35.0%)	26(46.4%)	251(32.4%)
1	452(63.0%)	21(37.5%)	452(58.4%)
2	71(9.9%)	9(16.1%)	71(9.2%)
Severity of immunodeposition in immunofluorescence
IgM deposition, n(%)				0.002*
0	94(1.2%)	6(10.7%)	94(12.1%)
1	15(2.1%)	0	15(1.9%)
2	460(64.1%)	22(39.3%)	460(59.4%)
3	188(26.2%)	26(46.4%)	188(24.3%)
4	17(2.4%)	2(3.6%)	17(2.2%)
C3 deposition, n(%)				0.049*
0	21(2.9%)	1(1.8%)	21(2.7%)
1	4(0.6%)	1(1.8%)	4(0.5%)
2	73(10.2%)	11(19.6%)	73(9.4%)
3	298(41.5%)	15(26.8%)	298(38.5%)
4	374(52.1%)	28(50%)	374(48.3%)
5	4(0.6%)	0	4(0.5%)
C1q deposition, n(%)				0.003*
0	622(86.6%)	38(67.9%)	622(80.4%)
1	25(3.5%)	3(5.4%)	26(3.4%)
2	117(16.3%)	11(19.6%)	117(15.1%)
3	10(1.4%)	4(7.1%)	10(1.3%)
Treatment
Glucocorticoids, n(%)				0.007*
Yes	628(87.5%)	53(94.6%)	628(81.1%)
No	90(12.5%)	3(5.4%)	146(18.9%)
Immunosuppressant, n(%)				0.103
Yes	618(86.1%)	40(71.4%)	618(79.8%)
No	100(13.9%)	16(28.6)	156(20.2%)
RAS inhibitor, n(%)				0.132
Yes	695(91.8%)	47(83.9%)	695(89.8%)
No	23(8.2%)	9(16.1%)	79(10.2%)

2 Clinical and pathological indicators and treatment of different deposition intensities of nephropathological IgM in patients with IgAN

Patients were classified into three categories based on the extent of IgM deposition in the glomerular mesangial area (refer to Fig. 2): the IgM-negative group, the low deposition group (IF ≤ 2+), and the high deposition group (IF > 2+). Clinical, histopathological characteristics, and treatment details for these groups were compared (see Table 2). The high IgM deposition group exhibited significantly lower serum albumin and eGFR levels, alongside higher cholesterol, 24-hour urine protein levels, and blood immunoglobulin M compared to the IgM-negative and low deposition groups. In terms of histopathology, the high deposition group showed more pronounced S-lesions, C3, and C1q deposition relative to the other groups.

Table 2

Clinical and histopathological characteristics of different deposition intensities of IgM in renal pathology of patients with IgAN. Note: All data are expressed as frequency (percentage), mean ± standard deviation, or median (interquartile range). *P < 0.05 is considered statistically significant. Abbreviations: SBP: systolic blood pressure; DBP: diastolic blood pressure; BMI: body mass index; HB: hemoglobin; Alb: serum albumin; TC: cholesterol; TG: triglycerides; LDL: low-density lipoprotein; HDL: high-density lipoprotein; UA: blood uric acid; Scr: serum creatinine; UTP: 24-hour urine protein quantification; M: increased mesangial cells; E: increased intracellular cells in capillaries; T: renal tubular atrophy or interstitial fibrosis; C: crescent formation; RAS: renin-angiotensin system inhibitors; URBC: microscopic examination of red blood cells (0 is less than 3/HP, 1 is 4–9/HP, 2 is 10–30/HP, 3 is greater than 30/HP); eGFR: estimated glomerular filtration rate; IgA, IgG, IgM, C3, C4: blood and fluid immune indicators. The severity of immunofluorescence was rated as 1 (-+), 2 (+), 3 (++), 4 (+++), 5 (++++).
Variables	Negative IgM deposition (n = 94)	Low IgM deposition (n = 475)	High IgM deposition (n = 205)	P-value
Age (years)	36.5[31,47]	36[29,45]	37[29,47]	0.216
Male, n(%)	44 (46.8%)	189 (39.8%)	73 (35.6%)	0.182
Time (months)	48[28.3,60]	48[30,60]	46[36,57]	0.936
BMI (kg/m²)	23.4[20.5,25.3]	22.5[20.3,24.6]	22.7[20.6,25.3]	0.146
SBP (mmHg)	122[112,134]	121[111,134]	124[112,137.5]	0.218
DBP (mmHg)	78[70,85.5]	77[68.9,85]	77[67.5,87]	0.770
HB (g/L)	120[111,136]	121[110,133]	119[109.5,130]	0.355
Alb (g/L)	38[35.6,40.9]	38.5[35.8,41]	37.3[33.8,39.5]	< 0.001*
TC (mmol/L)	4.3[3.6,5.0]	4.4[3.8,5.0]	4.6[4.0,5.4]	0.010*
TG (mmol/L)	1.3[0.8,1.7]	1.2[0.9,1.7]	1.2[0.9,1.8]	0.743
LDL (mmol/L)	2.7[2.2,3.1]	2.6[2.2,3.2]	2.8[2.2,3.4]	0.087
HDL (mmol/L)	1.0[0.8,1.3]	1.1[0.9,1.3]	1.1[0.9,1.3]	0.151
UA (umol/L)	323[261.8,372.8]	301[248,363]	306[252.5,363]	0.286
Scr (umol/L)	81[60,107.3]	73[58,101]	76[58.5,110.5]	0.065
24h-UTP (g/day)	0.9[0.4,1.5]	0.8[0.4,1.6]	1.1[0.6,2.3]	< 0.001*
URBC	1[0,3]	1[0,3]	1[0,3]	0.298
eGFR (ml· min^− 1· 1.73m^− 2)	81.3[60.9,108.6]	91.8[69.4,109.4]	80.5[55.6,107.8]	0.019*
IgG (g/L)	1080[869,1270]	1110[933.5,1280]	1060[879.8,1260]	0.195
IgA (g/L)	302[231.5,359.8]	293.5[240.3,364.8]	283.5[230.8,343]	0.245
IgM (g/L)	84[55.3,105.8]	103[79,136]	120[92.8,167.3]	< 0.001*
C3 (g/L)	97[87,106.8]	97[86,111]	95.5[80.8,109]	0.235
C4 (g/L)	23.5[18.3,26]	23[18.3,27]	22.5[18,27]	0.592
Optical microscope analysis
M, n(%)				0.850
0	0	5 (1%)	1 (0.5%)
1	74 (100%)	470 (99%)	204 (99.5%)
E, n(%)				0.600
0	51 (75.5%)	335 (70.5%)	144 (70.2%)
1	23 (24.5%)	140 (29.5%)	61 (29.8%)
S, n(%)				0.028*
0	23 (24.5%)	75 (15.8%)	25 (12.2%)
1	51 (75.5%)	400 (84.2%)	180 (87.8%)
T, n(%)				0.108
0	66 (70.2%)	358 (75.4%)	135 (65.9%)
1	22 (23.4%)	99 (20.8%)	60 (29.3%)
2	6 (6.4%)	18 (3.8%)	10(4.9%)
C, n(%)				0.239
0	39 (41.5%)	144 (30.3%)	68(33.2%)
1	48 (51.1%)	289 (60.8%)	115(56.1%)
2	7 (7.4%)	42 (8.8%)	22(10.7%)
Severity of immunodeposition in immunofluorescence
C3 deposition, n(%)				< 0.001*
0	7 (7.4%)	10 (2.1%)	4(2%)
1	0	3 (0.6%)	1(0.5%)
2	13 (13.8%)	49 (10.3%)	11(5.4%)
3	45 (47.8%)	199 (41.9%)	54(26.3%)
4	28 (29.8%)	212 (44.6%)	134(65.4%)
5	1 (1.1%)	1 (0.2%)	2(1%)
C1q deposition, n(%)				< 0.001*
0	90 (95.7%)	392 (82.5%)	139(67.8%)
1	0	17 (3.6%)	9(4.4%)
2	4 (4.3%)	64 (13.5%)	3(1.5%)
3	0	2 (0.4%)	8(3.9%)
Treatments and outcomes
Treatment, n(%)
Glucocorticoids, n(%)	72 (76.6%)	380 (80.0%)	176 (85.9%)	0.098
Immunosuppressant, n(%)	69 (37.4%)	381 (80.2%)	168 (82.0%)	0.215
RAS inhibitor, n(%)	88 (93.6%)	422 (88.8%)	185 (90.2%)	0.335
Number of final-entry events, n(%)	6 (6.4%)	22 (4.6%)	28 (13.7%)	< 0.001*

3 Patient survival curve analysis

Out of 774 patients, 718 had a favorable prognosis, while 56 reached the composite renal endpoint. The Kaplan-Meier survival curves indicated an overall adverse prognostic rate of 7.2% for IgAN at 5 years (Fig. 3A). Among the 774 patients, renal survival rates were 98.2% at 10 months, 97.4% at 20 months, 96.6% at 30 months, 95.6% at 40 months, 94.7% at 50 months, and 92.8% at 60 months. The Kaplan-Meier curves further revealed that patients with high IgM deposition exhibited significantly worse prognosis compared to those with negative and low IgM deposition (log-rank test P < 0.001) (Fig. 3B).

4 Cox regression analysis results

Univariate Cox analysis identified several renal factors influencing the composite endpoint, including age, blood pressure (systolic and diastolic), hemoglobin, serum albumin, cholesterol, triglycerides, LDL, blood uric acid, serum creatinine, 24h UTP, eGFR, blood IgG, renal pathology, complement C3, C4, and C1q deposition, E and T lesions, IgM deposition, glucocorticosteroids, and immunosuppressants (Table 3). Subsequent multivariate Cox regression analysis, incorporating significant variables from the univariate analysis via stepwise selection, demonstrated that immunosuppressant use (HR = 0.436, 95% CI 0.222–0.856, P = 0.016) served as an independent protective factor for IgAN prognosis. Conversely, low serum albumin levels (HR = 0.918, 95% CI 0.846–0.996, P = 0.039), T2 lesions (HR = 12.853, 95% CI 3.185–51.864, P < 0.001), and nephropathological IgM deposits (HR = 1.442, 95% CI 1.011–2.057, P = 0.043) were identified as independent risk factors for the 5-year prognosis of IgAN.

Table 3

Univariate and multivariate Cox regression models for composite renal endpoints (n = 774). Note: P < 0.05 is considered statistically significant. Abbreviations: 24h-UTP: 24-hour urine total protein; eGFR: estimated glomerular filtration rate; E: capillary cell proliferation; T: tubular atrophy or interstitial fibrosis.
Variables	Univariate analysis		Multivariate analysis
Variables	HR(95%Cl)	P-value	HR (95% Cl)	P-value
age	1.040(1.018–1.062)	< 0.001
SBP	1.031(1.019–1.042)	< 0.001
DBP	1.026(1.041–1.038)	< 0.001
HB	0.972(0.957–0.987)	< 0.001
Alb	0.887(0.857–0.919)	< 0.001	0.918(0.846–0.996)	0.039
TC	1.369(1.206–1.555)	< 0.001
TG	1.235(1.078–1.414)	0.002
LDL	1.304(1.157–1.469)	< 0.001
UA	1.009(1.005–1.012)	< 0.001
Scr	1.020(1.017–1.023)	< 0.001
24h-UTP	1.430(1.317–1.552)	< 0.001
eGFR	1.939(1.927–1.951)	< 0.001
IgG	0.999(0.998-1.000)	0.030
C4	1.045(1.012–1.078)	0.007
E
E0
E1	0.486(0.238–0.993)	0.048
T
T0
T1	8.240(3.830-17.728)	< 0.001
T2	75.480(34.647-164.436)	< 0.001	12.853(3.185–51.864)	< 0.001
IgM deposition	1.517(1.086–2.118)	0.014	1.442(1.011–2.057)	0.043
C1q deposition	1.396(1.062–1.837)	0.017
Glucocorticoids	3.753(1.173–12.013)	0.026
Immunosuppressant	0.550(0.308–0.983)	0.044	0.436(0.222–0.856)	0.016

IgAN represents the most prevalent form of primary glomerulonephritis, constituting 54.3% of primary glomerulonephritis cases confirmed by renal biopsy^[11]. Approximately 25–40% of patients with IgAN progress to ESRD within 10 to 20 years, necessitating renal replacement therapy^[12]. The disease is marked by considerable variability in clinical presentation, progression, and long-term outcomes^[13]. While numerous factors influencing the prognosis of IgAN have been identified, additional unknown factors remain to be uncovered. This study analyzed clinical and renal pathological data from 774 patients with IgAN to identify prognostic factors affecting their outcomes.

In this study, the cumulative renal survival rates at 10, 20, 30, 40, 50, and 60 months were 98.2%, 97.4%, 96.6%, 95.6%, 94.7%, and 92.8%, respectively, indicating a progressive disease course. Approximately 7.2% of patients progressed to ESRD within 5 years, aligning with the long-term follow-up results reported by Chang et al.^[14], who observed a composite endpoint occurrence in 27 out of 330 patients (8.2%) over a median follow-up period of 47.4 months. Recognizing that 30–40% of patients with IgAN may advance to ESRD within 10 to 25 years, a 5-year observation period may seem limited. However, the current international IgAN prognostic assessment tools aim to identify high-risk patients as early as possible, with a 5-year prediction window and an AUC of 0.9. Consequently, this study adopted a 5-year follow-up for composite endpoint events to promptly identify prognostic risk factors and facilitate early intervention to improve patient outcomes.

Recent intensive studies on IgAN have highlighted several emerging risk factors. Saleem et al. ^[5] conducted a retrospective analysis of 93 biopsy-confirmed primary IgAN cases, identifying T lesions as an independent risk factor for reaching the composite endpoint, both in univariate and multivariate analyses. Previous clinical research has consistently linked low serum albumin levels with poor renal prognosis ^[15][16][17]. Hypoalbuminemia may signal malnutrition, liver disease, chronic inflammation, or severe proteinuria^[16], though the precise mechanism underlying its correlation with IgAN prognosis requires further investigation. Moriyama et al.^[4] demonstrated that patients with E1, S1, or C1 lesions who received immunosuppressive therapy had markedly improved prognoses compared to those who did not. Immunosuppressive treatments not only reversed active glomerulopathy but also alleviated proteinuria and hematuria^[18]. A meta-analysis by Zheng et al.^[19] indicated that drugs such as acetazolamide (AZA), mycophenolate mofetil (MMF), leflunomide (LEF), cyclophosphamide (CTX), and tacrolimus (TAC) were effective in reducing proteinuria in patients with IgAN, with MMF being associated with fewer adverse effects compared to AZA, LEF, CTX, and TAC. However, some studies^[20] suggest that corticosteroids or immunosuppressive agents may not provide additional benefits over supportive therapy in patients with mild proteinuria. In this study, the Cox proportional hazards regression model identified T2 lesions (HR = 12.853, 95% CI 3.185–51.864, P < 0.001) as an independent risk factor for IgAN prognosis, while immunosuppressant use (HR = 0.436, 95% CI 0.222–0.856, P = 0.016) emerged as a protective factor. Lower serum albumin levels (HR = 0.918, 95% CI 0.846–0.996, P = 0.039) were also independently associated with poorer outcomes, aligning with findings from Song et al.^[16][17]. The study also revealed that hormone therapy did not offer significant prognostic benefits, a finding consistent with the STOP-IgAN study^[21] but contrasting with the TESTING study^[22]. This discrepancy may be attributed to differences in patient risk profiles; for instance, this study's cohort had a mean baseline proteinuria of 0.9 g/d and an eGFR of 88.9 mL/(min· 1.73 m²), whereas patients with STOP-IgAN had a mean baseline proteinuria of 1.8 g/d and an eGFR of 57.4 mL/(min· 1.73 m²), and the TESTING study cohort had mean proteinuria of 2.46 g/d and an eGFR of 61.5 mL/(min· 1.73 m²). This suggests that the mild disease severity in this study may have limited the observed efficacy of hormone treatments, while such therapies could significantly mitigate renal failure risk in high-risk IgAN individuals with substantial proteinuria and rapid progression.

In IgAN renal pathology, IgA staining typically correlates with C3 deposition and often occurs alongside IgG and/or IgM deposits. While extensive research has established a correlation between C3 and IgG deposits and prognosis, studies linking mesangial IgM deposits with morphological and clinical features of the Oxford classification remain limited^[23][24]. In this study, 87.9% of patients exhibited positive IgM deposits, while 12.1% had none, indicating a higher prevalence of IgM deposition in IgAN. Furthermore, nephropathological IgM deposition (HR = 1.442, 95% CI 1.011–0.057, P = 0.043) emerged as an independent risk factor for IgAN prognosis. Comparative analysis revealed that glomerular segmental sclerosis was more pronounced in the high IgM deposition group, suggesting an association between IgM deposits and segmental sclerosis, which adversely affects prognosis. Heybeli et al.^[25] demonstrated that IgM deposition in IgAN is linked with chronic lesions such as cluster adhesions, old glomerular sclerosis, and segmental sclerosis. This association may arise from the accumulation of IgM in sclerotic areas due to its size and its role in tissue repair ^[26]. In a study involving 30 patients with primary IgAN, a notable increase in IgM deposition was observed at the second renal biopsy (from 11/30 to 21/30 patients), while complement deposits like IgA and IgG remained unchanged^[27]. This secondary IgM 'deep deposition,' rather than mere 'co-deposition' with C3 or IgG, might drive IgAN progression, as patients with IgM deposits showed higher rates of glomerulosclerosis and severe tubulointerstitial disease^[28]. IgM is known to activate the lectin pathway during ischemia/reperfusion injuries in various organs, including the kidney, by binding to antigens and exposing carbohydrate patterns that activate mannose-binding lectin (MBL), leading to further complement activation^[29]. Recent findings by Heybeli et al. ^[25][30] highlight that activation of C4d in the lectin pathway is an independent risk factor for progression to ESKD in patients with IgAN. This study also found a correlation between renal IgM deposition and C4d staining, suggesting that IgM might activate both the classical and lectin complement pathways, influencing IgAN progression. Lloyd et al.^[31] proposed that immune complex deposition, such as IgM, in the glomerular mesangial area might be linked to subclinical infections, and reducing IgM deposits could potentially slow IgAN progression. The combined evidence suggests that IgM deposition in the mesangial region is associated with more severe chronic renal pathology. However, whether IgM deposition causes kidney damage or if it reflects secondary changes due to renal pathology remains unclear. Clarifying this causal relationship could lead to the development of targeted treatments for IgAN.

The phenomenon of IgM deposition is not exclusive to IgAN but also occurs in focal segmental glomerulosclerosis (FSGS). Strassheim et al.^[32] proposed that in the context of non-immune injury, newly exposed epitopes may attract IgM, which could lead to complement deposition and subsequent glomerular damage. Furthermore, Zhang et al.^[33] demonstrated that the co-localization of IgM and C3 in the glomeruli of patients with primary FSGS was independently associated with poorer therapeutic responses and renal outcomes. These findings underscore the significant role of IgM deposition in a range of glomerular diseases and suggest potential shared mechanistic pathways between IgAN and FSGS.

However, this study has several limitations: (1) Being retrospective and observational, it may not fully account for all residual confounders. (2) The single-center nature and limited sample size of the study may restrict the generalizability of the findings to the broader IgAN population. (3) The follow-up period was relatively short, potentially affecting the assessment of long-term prognosis for patients with IgAN. (4) The study only assessed the correlation between IgM deposition in the mesangial area and IgAN prognosis without exploring underlying mechanisms in depth. Future research will aim to address these limitations by increasing the sample size, extending the follow-up duration, and examining additional influencing factors. Additionally, further studies will explore the pathological significance of IgM deposition in IgAN.

In summary, this study reveals that the use of immunosuppressive agents enhances the 5-year prognosis of IgAN, as evidenced by traditional clinical and nephropathological indicators. Besides the commonly recognized independent risk factors of low serum albumin and T2 lesions, mesangial IgM deposition also stands out as an independent prognostic factor for IgAN over five years.

Ethical approval and consent to participate:Approved by the Ethics Committee of Hangzhou Hospital of Traditional Chinese Medicine, this retrospective study exempted participants Approved by the Ethics Committee of Hangzhou Hospital of Traditional Chinese Medicine, this retrospective study exempted participants from signing informed consent (ethics number: 2021KY045).

Consent for publication:Not applicable.

Availability of data and materials:The datasets used and analyzed during the current study are available from the corresponding author upon reasonable request.

Competing interests:The authors declare that they have no competing interests

Funding:This study was funded by the National Natural Science Foundation of China (82205008); Hangzhou Municipal Health Commission Project (A20210083); Project of Zhejiang Provincial Administration of Traditional Chinese Medicine (2023ZF137); Key Research Project of Zhejiang University of Traditional Chinese Medicine Affiliated Hospital (2022FSYZZ14); Zhejiang Provincial Department of Health Project (2023RC242);Zhejiang Provincial Public Welfare Fund Project(LTGY23H270007).

Authors' contributions:XZ, MJ and CY analyzed and interpreted data from relevant IgAN patients, XL and DY performed the histology of the kidneys, LG was the main contributor to writing the manuscript, and QZ provided financial support and reviewed the manuscript. All authors read and approved the final manuscript

Acknowledgements:The author would like to thank the Nephrology Laboratory of Hangzhou Hospital of Traditional Chinese Medicine, affiliated with Zhejiang University of Chinese Medicine, for their support in this study.We thank Bullet Edits Limited for the linguistic editing and proofreading of the manuscript.

Clinical trial number: not applicable.

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No competing interests reported.

Relationship between IgM deposition intensity in renal tissue and 5-year renal prognosis in immunoglobulin A nephropathy

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Abstract

Figures

Introduction

Object and method

1 Research object

2 Clinical and laboratory data

3 Histopathological data

4 Treatment, endpoints, and follow-up

5 Statistical Analysis

Result

Discussion

Declarations

References

Additional Declarations

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Version 1