Allergic bronchopulmonary aspergillosis (ABPA) occurs as a complication in patients with cystic fibrosis (CF). Previous studies of the immunopathogenesis of ABPA have indicated that B cells (IgG and IgE antibodies to Aspergillus fumigatus), T cells, and eosinophils are components of the disease. To evaluate T-cell regulation, we examined in vitro immune responses in seven patients with CF and ABPA compared with subjects who had a positive reaction to an A. fumigatus (Af) prick skin test, an IgG precipitating antibody test, or both (ST/PPT), and with subjects with CF who had negative prick skin test results and precipitating antibodies to Af (Af negative). Analyses of T-cell phenotypes revealed that patients with CF and ABPA compared with patients with CF who had ST/PPT positive and Af negative results had slightly increased percentages of T-helper cells, 50.1% versus 43.0% (p not significant) and 42.2 (p less than 0.025), respectively, but comparable percentages and numbers of T-suppressor cells. Serum IgE concentrations were significantly increased in subjects with CF and ABPA versus both subjects who had ST/PPT-positive and Af-negative results, 2916 versus 281 and 73 IU/ml (p less than 0.001 and less than 0.001, respectively). In addition, B cells from patients with CF and ABPA had significantly increased in vitro preformed IgE (p less than 0.01) and increased spontaneous de novo IgE spontaneous synthesis compared with cells from subjects who had ST/PPT positive and Af-negative results (p less than 0.01 and less than 0.01), indicating prior in vivo activation.(ABSTRACT TRUNCATED AT 250 WORDS)