The presence of C. pneumoniae specific T lymphocytes among in vivo activated cells from the AAA tissue specimens suggests that C. pneumoniae participates in the maintenance of the inflammatory response in the tissue and may thus be involved in the progression of the disease.

The development of Chlamydia pneumoniae-specific cell-mediated immunity was studied during a primary C. pneumoniae infection. The immune response was detected as positive lymphocyte proliferation and secretion of interferon gamma.C. pneumoniae-induced activation of both CD4+and CD8+ T cells was detected in the early phase of infection, but activation of only CD4+ T cells was detected in the later stage.

Marked cell-mediated and humoral immunity to C. pneumoniae in males with coronary heart disease suggest that the immune mechanisms triggered by Chlamydia are a possible contributing factor in the disease pathogenesis of coronary atherosclerosis in males. The Chlamydia-specific cell-mediated responses seem to be predominantly induced by antigenic structures that are similar among different Chlamydia-species.