The role of IgA and IgG in Mycobacterium tuberculosis infection: a cross-sectional study in Ethiopia.

INTRODUCTION

Despite the high global prevalence of Mycobacterium tuberculosis (Mtb) infection in humans, most infected individuals achieve a stable immunological equilibrium, without showing clinical signs and symptoms of tuberculosis (TB). Although the role of antibodies in TB is assumed to be relatively small compared with cell-mediated immunity, their role in TB has been documented in a few recent studies.

METHODS

In this cross-sectional study, we quantitated antibody responses to Mtb antigens, lipoarabinomannan (LAM), and heparin-binding hemagglutinin adhesin (HBHA) by determining antigen-specific immunoglobulin A(IgA) and G(IgG) secretion levels using enzyme-linked immunosorbent assay in serum and saliva of pulmonary TB patients (PTB), their household contacts, and community controls (determined by QuantiFERON TB Gold assay QFT-test result).

RESULTS

The HBHA-specific IgA levels were significantly higher in both saliva and serum in household contacts groups compared with PTB patients (P = 0.013, P = 0.023). Exposed contacts, who were QFT-negative, had higher serum HBHA-specific IgA responses compared with PTB patients (P = 0.04). QFT-negative household contacts and QFT-positive community controls showed higher HBHA and lipoarabinomannan-specific IgG responses (P = 0.006, P = 0.002, P = 0.0009, P = 0.006, respectively) than PTB patients. Generally, lipoarabinomannan and HBHA-specific IgA levels were significantly higher in saliva compared with serum (P < 0.0001) in all study groups.

CONCLUSION

Overall, the observed higher levels of IgA and IgG in controls, and exposed but QFT-negative contacts suggest a correlation with, and perhaps a role for these antibodies in preventing the development of active TB. The findings highlighted the potential involvement of saliva IgA in the immune response to Mtb, underscoring the relevance of mucosal immunity in TB infection.