Humoral immune response against mycobacterial antigens in bronchoalveolar fluid from tuberculosis patients

Resistance to tuberculosis (TB) is cell-mediated but a humoral response is common and may be correlated with the lack of effective local cellular defense mechanisms. The goal of the study was to evaluate IgG, IgA, and IgM-mediated humoral immune response against 38-kDa+16-kDa and 38-kDa+lipoarabinomannan (LAM) mycobacterial antigens in bronchoalveolar fluid (BALF) from patients with pulmonary TB. Non-tuberculosis (NTB) patients were used as control. 179 BALF samples (56 TB and 123 NTB) were examined. Commercially available ELISA-based assays against proteins 38-kDa and 16-kDa or 38-kDa plus LAM were used. Three different dilutions of BALF: 1:1; 1:10, and 1:50 (100) were tested. Only the results obtained with the 1:10 dilution allowed distinguishing TB and NTB groups. The mean IgG level for 38-Da+LAM was significantly higher in the TB than that in the NTB group (P<0.0001). The mean IgA level for 38-kDa+LAM also was higher in the TB group (P<0.05). No difference was observed between TB and NTB groups in the titer of IgM antibodies. These findings indicate that TB is associated with the presence of detectable levels of antibodies in BALF. The antibody response is highly heterogeneous. This phenomenon results from the balance between pathogen and host immune system. The tests examined for detection of IgG in BALF can be used in combination with other diagnostic methods to increase diagnostic accuracy of pulmonary TB.