Chlamydial respiratory infection in childhood and spurious immunoglobulin M.

The role of Chlamydia trachomatis was investigated in lower respiratory tract infections in 254 children. The organism was not isolated in any child but Bordetella pertussis was isolated from 65. Two of the latter and one of the remaining 189 children with negative isolation, however, had immunoglobulin M (IgM) antibodies to Chlamydia trachomatis (titers of 1:64, 1:64 and 1:128). Exhaustive absorption of the sera with bordetella antigen left the chlamydial titers unchanged, thus excluding the possibility of cross-reactivity with bordetella antigen. To determine whether nonspecific stimulation of B lymphocytes played a role, sera from 72 children with infectious mononucleosis were examined. Chlamydial IgM antibodies (greater than or equal to 1:64) were detected in 14 of these sera, significantly more often than in other acute childhood infections (p = 0.002). Serotyping showed that these antibodies had a heterogeneous specificity in different sera and a reactivity pattern suggesting they were monoclonal. The association found between chlamydial IgM antibodies and Epstein-Barr virus infection implies that there is nonspecific production of these antibodies in infectious mononucleosis, suggesting that similar nonspecific antibody production could occur in other infections. This might explain the chlamydial IgM found in children with lower respiratory tract infections in whom chlamydial infection could not be confirmed by isolation.