Background: One of the widely used diagnostic methods for Mycobacterium tuberculosis (MTB) infection is the acid-fast bacilli staining of formalin-fixed paraffin-embedded (FFPE) tissues; however, this method cannot discriminate between MTB and nontuberculous mycobacteria (NTM) species. Moreover, confirming tuberculosis (TB) using FFPE tissue specimens may be difficult owing to their low bacterial load. In addition, interference in molecular diagnostic assays, including polymerase chain reaction (PCR), may occur owing to fragmentation and genomic DNA cross-linkage in FFPE tissues formed during formalin fixation or paraffin-embedding procedures. Therefore, we aimed to investigate whether an automated molecular diagnostic method based on PCR-reverse blot hybridization assay can discriminate between human MTB-positive and -negative FFPE tissues and to compare the relative mRNA expression levels of various host immune markers between MTB-infected and uninfected human tissues using quantitative reverse transcription (qRT) PCR. A total of 52 human FFPE tissue samples from various regions of the body, including the lungs, lymph nodes, tendons, colon, and appendix, were collected and used for the molecular identification of Mycobacterium species and analysis of cytokine mRNA expression.
Results: IFN-γ, TNF-α, IP-10, CXCL9, CXCL11, and GM-CSF mRNA expression levels in MTB-infected tissues were significantly higher than those in uninfected samples. Additionally, the differences in the mRNA expression levels of IFN-γ, CXCL9, and GM-CSF between MTB-infected and uninfected tissues were statistically significant were statistically significant (p < 0.05). Correlation curve analysis indicated that the mRNA expression of IFN-γ was inversely proportional to that of IP-10 and that the mRNA expression levels of IFN-γ, TNF-α, CXCL9, CXCL11, GM-CSF, and TNFR were proportional and well-correlated. Furthermore, to establish marker profiles for detecting MTB infection, the statistically significant expression levels of three markers were combined. We confirmed that the combined profile of IFN-γ, CXCL9, and GM-CSF expression levels was statistically significant (P < 0.001).
Conclusions: Although the mRNA expression patterns of host immune markers may vary according to MTB infection status, these patterns may be highly correlated and can be simultaneously used as an additional indicator for diagnosing TB in human tissue samples.