BAL and Serum IgG Levels in Healthy Asymptomatic HIV-infected Patients

Objectives: To determine if the increased susceptibility to bacterial infection in asymptomatic HIV-infected patients is associated with decreased total IgG or IgG2 levels in lung epithelial lining fluid.

Background: A decrease in lung IgG levels or subtypes has been proposed as contributing to the increased risk of bacterial lung infections in HIV-infected patients. Previous studies measuring lung lavage IgG concentrations have been inconsistent.

Methods: Twenty-three HIV patients and 25 control subjects underwent BAL. Both patient groups were of similar age, and had similar pulmonary function studies and body mass index. Smokers were equally represented in both groups, and the majority of subjects in both groups were male. Total IgG and IgG2 levels in lavage fluid were assayed in both cohorts and compared using a two-tailed Student's t test.

Results: The lung lining fluid IgG level in HIV-infected patients was 0.19 +/- 0.13 microg/microg of protein (mean +/- SD) vs 0.11 +/- 0.09 microg/microg of protein in control subjects (p < 0.05). The IgG(2) level in HIV patients was 0.034 +/- 0.038 microg/microg of protein and 0.014 +/- 0.01 microg/microg of protein in control subjects (p = 0.054). Lavage IgG levels reflected serum IgG values (correlation coefficient, 0.56; p < 0.001) but did not correlate with lung immunoglobulin-producing cells.

Conclusions: The increased susceptibility to bacterial pneumonia in asymptomatic HIV-infected individuals is neither explained by depressed total IgG levels nor a deficiency in IgG(2) levels in the lungs. The strong correlation between serum and lavage IgG levels suggests that lavage IgG derives from serum.