LOCAL IMMUNE-RESPONSES TO CHLAMYDIA-PNEUMONIAE IN THE LUNGS OF BALB CMICE DURING PRIMARY INFECTION AND REINFECTION/

Cell-mediated immune (CMI) responses play a major role in protection a s well as pathogenesis of many intracellular bacterial infections. In this study, we evaluated the infection kinetics and assessed histologi cally the lymphoid reactions and local, in vitro-restimulated CMI resp onses in lungs of BALB/c mice, during both primary infection and reinf ection with Chlamydia pneumoniae. The primary challenge resulted in a self-restricted infection with elimination of culturable bacteria by d ay 27 after challenge, A mild lymphoid reaction characterized the path ology in the lungs. In vitro CMI responses consisted of a weak prolife rative response and no secretion of gamma interferon (IFN-gamma), The number of lung-derived mononuclear cells increased substantially durin g the primary infection; the largest relative increase was observed in B cells (B220(+)). After reinfection, the number of lung-derived mono nuclear cells increased further, and the response consisted mainly of T cells. The reinfection was characterized in vivo by significant prot ection from infection (fewer cultivable bacteria in the lungs for a sh orter period of time) but increased local lymphoid reaction at the inf ection site. In vitro, as opposed to the response in naive mice, acqui red immunity was characterized by a strongly Th1-biased (IFN-gamma) CM I response. These results suggest that repeated infections with C. pne umoniae may induce Th1-type responses with similar associated tissue r eactions, as shown in C. trachomatis infection models.