Figure 3
Immune protection against chlamydial infection in the female genital tract. Innate, humoral, and cell-mediated immunity act in concert to protect against C. trachomatis infection of non-immune host genital epithelial cells and local innate immune cells in the female genital tract. The hormones estradiol and progesterone regulate innate and adaptive immunity against genital Chlamydia by promoting mucus secretions, regulating immune and non-immune cell numbers and activities (Figure 2), and by altering cell receptor expression at this mucosal site. Innate: The epithelial barrier is relatively ineffective at protecting against Chlamydia as this mucosal pathogen has a myriad of mechanisms to evade barrier protection. A mucus layer containing a variety of antimicrobial factors and endogenous microbiota contributes towards regulating the pH of the FGT to protect against genital tract pathogens. Innate immune cells constitutively secrete an array of soluble antimicrobials, including secretory leukocyte protease inhibitor (SLPI), human β-defensin 2 (HBD2), lysozyme, lactoferrin, Elafin, cathelicidins. Chlamydial infection of columnar epithelial cells and local genital tract immune cells, including neutrophils, macrophages, and natural killer (NK) cells, produces soluble antimicrobials,chemokines, and pro-inflammatory cytokines that selectively prevent bacterial infection of target host cells. (e.g., interleukin (IL)-1 released from infected epithelial cells promotes T helper type 17 (Th17) differentiation). Recruitment and activation of adaptive immune cells (B and T cells) are also orchestrated by the release of these secreted soluble antimicrobial factors from epithelial cells, dendritic cells, and macrophages. Humoral: Antibodies potentially can prevent infection by Chlamydia. Immunoglobulin G (IgG) is the predominant antibody in the FGT. Antibodies released from plasma cells (P IgG and P IgA) inactivate extracellular chlamydial elementary bodies. Cell-mediated: CD4+ T-cell production of interferon (IFN)-γ contributes to host defence by inhibiting intracellular chlamydial replication. Cell-mediated immunity induces apoptosis of infected cells by cytotoxic CD8+ T cells.6, 20, 35, 39, 40, 62, 63, 77, 117, 118, 119, 150, 151, 152, 153, 154, 155, 156, 157, 172 CTL, cytotoxic T lymphocyte; GM-CSF, granulocyte-macrophages colony-stimulating factor; MMP, matrix metalloproteinase; GRO-α, growth related oncogene-α; TNF, tumor necrosis factor; Treg, regulatory T cell.
