Serologic markers for Chlamydia pneumoniae in asthma

Background: Chlamydia pneumoniae infection has been reported as a possible etiologic agent in asthma, which in primary care settings often appears to be initiated by acute respiratory infections. Objective: To determine if serologic markers for C. pneumoniae are associat ed with adult asthma that first became symptomatic after an acute respirato ry illness (asthma associated with infection: AAWI). Methods: Serum samples from 164 primary care outpatients, mean age 44 years , (68 with AAWI; 36 with atopic, occupational or exercise-induced asthma (n on-AAWI); 16 nonasthmatic patients with acute bronchitis; and 44 asymptomat ic nonasthmatic controls) were tested for the presence of C, pneumoniae-spe cific IgG and IgA antibodies. Levels of chlamydial heat shock protein 60 (C HSP60) antibody were also measured. Those positive for CHSP60 were tested f or C, pneumoniae-specific IgE antibodies by immunoblotting. Results: Statistically significant differences in IgG and IgA seroreactivit y were noted between groups: acute bronchitis and AAWI had the highest leve ls (93% to 94% IgG seroreactivity, 69% to 75% IgA seroreactivity) whereas n on-AAWI and asymptomatic controls had the lowest levels (61% to 84% IgG ser oreactivity, 31% to 43% IgA seroreactivity, P < .02 after adjustment for ag e, sex and smoking). CHSP60 antibodies were significantly more prevalent in AAWI than in non-AAWI (19% versus 3%, P = .02). IgE antibodies against C. pneumoniae 60, 62, and/or 70 kD antigens were detected in 5 of 13 CHSP60 po sitive AAWI patients. Persistent IgG, IgA, and CHSP60 seroreactivities were noted in all seropositive asthma patients with serial serum samples. Conclusions: Serologic markers of C. pneumoniae infection were associated w ith acute bronchitis and with asthma that first became symptomatic followin g respiratory illness. Serologic responses to C. pneumoniae may be useful i n the classification and diagnosis of asthma.