Changes in Serum IgA Antibody Levels against the Glycopeptidolipid Core Antigen during Antibiotic Treatment of Mycobacterium avium Complex Lung Disease.

We evaluated serial changes in the levels of serum immunoglobulin A (IgA) antibody to the glycopeptidolipid (GPL) core antigen during antibiotic treatment in 57 patients with Mycobacterium avium complex (MAC) lung disease at baseline (T0) and after 3 months (T3) and 6 months (T6) of treatment. The median patient age was 59 years, and 37 (65%) patients were women. The etiologic organisms included M. avium in 32 (56%) patients and M. intracellulare in 25 (44%) patients. Seven (12%) patients had the fibrocavitary form of the disease on computed tomography. After 12 months of treatment, 42 (74%) patients had a favorable response to treatment, whereas 15 (26%) patients had an unfavorable response to treatment defined as the absence of sputum culture conversion within 12 months of treatment. The initial median serum anti-GPL IgA levels in the 57 patients was 3.50 U/mL, and the antibody levels at T0 (median 3.50 U/mL), T3 (median 2.71 U/mL), and T6 (median 2.61 U/mL) were significantly decreased following treatment (P ＜ 0.001). The results of the multivariate analysis indicated that an initially elevated anti-GPL IgA level (＞ 3.50 U/mL) was associated with an unfavorable response (P = 0.049). Our data suggest that elevated anti-GPL IgA levels may reflect disease activity and may help predict treatment response in patients with MAC lung disease.