Participants and specimens
Serum samples were collected from seven patients with PV (Table 1) and three healthy volunteers. All the patients were in the active stage of the disease without treatment and met PV diagnostic criteria as follows: (i) multiple flaccid, easily ruptured bullae on the basic of mucocutaneous erythema, (ii) progressive refractory erosions covered crust secondary to blisters, (iii) positive Nikolsky’s sign, (iv) histopathological finding of intraepidermal blister formation, and (v) immunological feature of reticular bright green fluorescence IgG deposition on keratinocyte cells. We used the sera of healthy volunteers as control and inclusion criteria of PV as follows: (i) consistent with the diagnostic criteria for PV; (ii) neither immunosuppressant nor glucocorticosteroid was used in the last 30 days; (iii) without other autoimmune diseases, except for PV; and (iv) no significant organ dysfunction, as well as informed consent. Exclusion criteria are as follows: (i) PV patient is pregnant, (ii) pemphigus induced by drugs, (iii) patients with malignant tumor, and (iv) administration of tetracycline and macrolide antibiotics in the last month.
Cell culture and study design
The human keratinocyte cell line HaCaT (MssBio Co., Ltd. Guanzhou, China) was used to establish an in vitro model of PV according to a previous study[9].
Cells were cultured in Dulbecco’s modified Eagle’s medium (DMEM) (Hyclone, Cat. No. SH30022.01B) supplemented with penicillin (50 U/ mL, Hyclone, Cat. No. SH30010) with 10% fetal calf serum ( Hyclone, Cat. No.SH30087.0), then seeded at a density of 2 ×105 cells/cm2 on 25-mm2 cell culture flasks at 37°C in a humidified atmosphere containing 5% CO2. The culture medium was changed every 24 h until the cultures reached 80% confluency. The HaCaT cells were subcultured in 12-well plates up to 80% confluency. The 3rd passages of HaCaT cells were cultured continuously for 24 h in DMEM high glucose medium containing 5% PV-sera at 37°C in a humid, 5% CO2 incubator. For tacrolimus studies, cells were incubated in 5% PV-sera with 100 nM tacrolimus or NH sera with 100 nM tacrolimus (Absin Bioscience, China). The cells were harvested after 24 h, and total mRNA was extracted for analysis. Six experimental groups were designed in the study: control group (cells were incubated with medium without treatment), normal healthy (NH) sera group (cells were incubated with sera from healthy donors), PV-sera group (cells exposed to 5% PV-sera), positive group (cells were incubated with Dsg3 monoclonal antibody containing culture medium), PV-sera + FK506 group (cells were incubated with tacrolimus-treated and 5% PV-sera), and healthy-sera + FK506 group (cells were incubated with tacrolimus-treated and NH-sera).
Total RNA was extracted from the HaCaT cells using TRIzol reagent. First-strand cDNA synthesis was performed using a kit and following the manufacturer’s instructions. Using NCBI for RT- PCR primer design, the primer sequences for amplification of the Dsg1 (NCBI reference sequence: NM_001942), Dsg3 (NM_001944), and GAPDH (NM_001289746) gene fragments are shown in Table 2. The reaction volume was 20 μL and prepared as follows: 5 μL of cDNA template (1:10 dilution, ViiA7 software), 0.5 μL of the upstream primer, 0.5 μL of the downstream primer, 10 μL of SYBR® Premix Ex Taq™ (Tli RNase H Plus) (2×), and 4.0 μL of ddH2O. PCR cycling conditions were as follows: incubation 95°C for 30s min, followed by 40 cycles of 95°C for 3 s and 60°C for 34 s, with the addition of 60°C 1 min for elongation.
Western blot analysis of Dsg expression
The HaCaT cells were grown in 12-well plates for 18 h, the medium was replaced with DMEM containing 5% PV-sera or NH sera, and incubated for another 18 h, then 1×108 to 1×109 cells were collected for western blot analysis. The primary antibodies used were mouse anti-Dsg3 antibody (1:160 dilution; Abcam, Cambridge, UK) and mouse anti-Dsg1 antibody (1:500 dilution; Abcam). Goat anti-mouse antibody (1:1,000 dilution, Alexa Fluor-488, Thermo Fisher Scientific, Dreieich, Germany) served as secondary antibody.
Indirect immunofluorescence (IIF) detection of Dsg in HaCaT cells
The cells were grown directly (1× 105 cells/ml) on glass coverslips for 4 h in a 12-well plate and then continuously for 24 h after replacing the medium with or without supplements as earlier described. After washing with phosphate-buffered saline (PBS), the cells were fixed in 4% paraformaldehyde solution for 30 min. The samples were then washed thrice with PBS for 5 min each time. The cells were then permeabilized with 0.2% Triton X-100 for 5 min. After three rinses with PBS, the samples were blocked using 10% normal goat serum for 30 min. Then, the samples were incubated with the primary antibody (Dsg1 at 1:500 dilution; Dsg3 at 1:160 dilution) at 4°C overnight. As secondary antibody, fluorescently labeled goat anti-mouse antibodies were used at a dilution of 1:1,000 for 1 h at room temperature. The anti-Dsg1 and anti-Dsg3 antibodies were used against cell surface proteins Dsg1 and Dsg3. The nuclei were stained with 4′,6-diamidine-2′-phenylindole dihydrochloride (DAPI). Images of the cells morphology were captured by standard light microscopy. An inverted fluorescence microscope (DMI6000B, Leica, Japan) was used for image acquisition at 40× magnification. Average OD value was assayed by Image-Pro Plus 6.0 software (Media Cybernetics, Inc., Rockville, MD, USA)
Statistical analysis
Western blot analysis was visualized using ImageJ (NIH, USA). Statistical significance was assessed using one-way ANOVA followed by Bonferroni correction using GraphPad Prism 5 (GraphPad Software, La Jolla, CA, USA) for comparison of multiple groups. Differences were deemed significant when the calculated p value was <0.05. The data were expressed as the mean ± SD.