Abstract
Following the chlamydial exposure, a series of events occur in the host belonging to the innate and adaptive immune systems. The first line of defense against chlamydial infections is mucosal secretions contain various antimicrobial peptides. The complement system that can be part of defense is triggered by elementary bodies of Chlamydiae. Chlamydiae that escape from the complement system infect the epithelial cells. Chlamydiae are protected from phagolysosome fusion by generating inclusion formation. However, they are recognized by pattern recognition receptors (PRR), mainly Toll-like receptor 2. Chlamydia-PRR interaction can be resulted by cytokine/chemokine secretion. The first innate immune cells that reach the infection site are natural killer (NK) cells and neutrophils. The most important contribution of NK cells to this pathogen is the production of high levels of IFNγ. Neutrophils are effective in reducing the load of Chlamydia and shortening the duration of infection. The relationship of neutrophils with pathology is also discussed. Recognition of MHC class II-restricted Chlamydia peptides presented by dendritic cells via CD4 T cells initiates an adaptive immune response. IFNγ-mediated Th1 immune response is essential for Chlamydia clearance. CD8 T cells, which are fewer in numbers, have been suggested that they are the main cause of infection-related immunopathology. B cells and antibodies were found to be particularly effective in preventing reinfection.