F-30 Changes in serum levels of IgA antibody against the glycopeptidolipid core antigen during antibiotic treatment of Mycobacterium avium complex lung disease

Mycobacterium avium complex (MAC) is the most common causative agent of nontuberculous mycobacterial lung disease. An enzyme immunoassay that detects serum immunoglobulin A (IgA) antibodies against the glycopeptidolipid (GPL) core is used to diagnose MAC lung disease. However, how IgA levels change following MAC treatment, and the association between treatment response and initial IgA levels, remain poorly understood. We measured serum levels of the IgA antibody in 57 patients with MAC lung disease following 0 (T0), 3 (T3), and 6 months (T6) of treatment. Evaluations assessed whether elevated T0 IgA levels were associated with an unfavorable response, which was defined as failure of a negative culture conversion following 12 months of treatment. Of 57 patients, the median IgA levels at T0, T3, and T6 were 3.50 U/mL (interquartile range [IQR], 1.60-9.85 U/mL), 2.71 U/mL (IQR, 1.12-8.54 U/mL), and 2.61 U/mL (IQR, 0.96-6.35 U/mL), respectively, and were significantly reduced by treatment (P 3.50 U/mL) significantly increased the risk for an unfavorable response (P=0.038). In conclusion, serum levels of IgA targeting the GPL core antigen decrease following antibiotic treatment, suggesting that IgA levels may reflect disease activity and can help to predict treatment responses in MAC lung disease.