Fig. 3. CT135 induces neutrophil cytotoxicity to evade innate host defense.

a–f Knock out mice or antibody-treated RAG2^−/− mice were infected with CtD or CtD CT135⁻ at day 7 pi. a Mouse IgG and anti-Ly6G. b Control clodronate and liposomal clodronate. c RAG2^−/− and ILC^−/−RAG2^−/− mice. d Mouse IgG and anti-IFNγ. e RAG2^−/− and Perforin^−/−RAG2^−/− mice. f Mouse IgG and anti-IFN-α/β R1. Depletion of neutrophils specific rescued the infectivity of CtD CT135⁻. (a–f n = 5 mice per group, two-tailed Mann–Whitney test). g LDH release by bone marrow-derived neutrophils (BMDN) infected with different multiplicity of infection (MOI) of CtD and CtD CT135⁻. (Two-tailed unpaired student’s t tests). h LDH release in CtD infected BMDN is dependent on chlamydial de novo mRNA synthesis. i IL-1β secretion of BMDN infected with CtD, CtD CT135⁻ and CtD CT135⁻:: bla CT135. Anhydrotetracycline hydrochloride (aTC) (50 ng/ml) was added to BMDN prior- and post-infection for the induction of CT135. (h, i two-tailed Mann–Whitney test). g–i Result shown are representatives of two independent experiments. j Transmission electron micrographs of mock, CtD, and CtD CT135⁻ infected BMDN. Arrows denote inclusions containing chlamydiae undergoing early partial developmental reorganization. Pictures shown are representatives of two independent experiments. k Schematic model of chlamydial infection of uterine epithelial cells and interaction with neutrophils as a mechanism to evade neutrophil host defense. Lysed infected epithelial cells release numerous infectious EBs that are phagocytized by luminal neutrophils. Infection of neutrophils is abortive resulting in partial chlamydial development that is sufficient to cause cytotoxic death and promote IL-1β secretion. The ability to kill neutrophils allows CtD organisms to evade neutrophil host defense and sustain chronic infection of the uterine epithelial cells. a–i Data are shown as the mean ± SD.