Chlamydia pneumoniae in HIV-infected patients and controls assessed by a novel whole blood interferon-γ assay, serology and PCR

Chlamydia pneumoniae seropositivity is associated with cardiovascular disease and HIV infection. Cell-mediated immune responses are important for control of C. pneumoniae, and such responses may be impaired in HIV-infected patients. An assay for detection of interferon (IFN)-γ in whole blood stimulated with C. pneumoniae antigen was developed and studied in HIV-infected patients and uninfected controls. Among 34 HIV-infected patients, none had an IFN-γ response to C. pneumoniae antigen, compared with five of 32 healthy controls (p <0.001). Fewer HIV-infected individuals elicited a serum IgG response when tested with a commercial enzyme immunoassay (p 0.009), but this was not so for serum IgA (p 0.12). Additionally, the IFN-γ and antibody assays showed a trend towards a bivariate response in normal controls. This indicates that cellular and antibody responses against C. pneumoniae may be mutually exclusive, with potential implications for the role of this organism in the genesis of cardiovascular disease in both immunocompetent and HIV-infected populations.