Influx of Podoplanin-expressing inflammatory macrophages into the genital tract following Chlamydia infection.

Genital Chlamydia trachomatis infection remains a major health issue as it causes severe complications including pelvic inflammatory disease, ectopic pregnancy, and infertility in females as a result of infection-associated chronic inflammation. Podoplanin, a transmembrane receptor has been previously reported on inflammatory macrophages. Thus, strategies to specifically target podoplanin, might be able to reduce local inflammation. This study investigated the expression level and function of podoplanin in C. trachomatis infection model. C57BL/6 mice infected with mouse pathogen C. muridarum were examined intermittently from day 1 to day 60 using flow cytometrical analysis. Percentages of conventional macrophages (CD11b + CD11c - F4/80 + ) versus inflammatory macrophages (CD11b + CD11c + F4/80 + ), and the expression of podoplanin in these cells were investigated. Subsequently, a podoplanin knockout RAW264.7 cell was utilized to evaluate the function of podoplanin in C. trachomatis infection. Our findings demonstrated an increased CD11b + cell volume in spleen at day 9 post infection, with augmented podoplanin expression, especially among the inflammatory macrophages. A large number of podoplanin-expressing macrophages were detected in the genital tract of C. muridarum infected mice. Furthermore, analysis of the C. tachomatis-infected patients demonstrated a higher percentage of Podoplanin-expressing monocytes than that the non-infected controls. Using an in vitro infection in a transwell migration assay, we identified that macrophages deficient in podoplanin displayed defective migratory function towards C. trachomatis infected HeLa229 cells. Lastly, using immunoprecipitation-mass spectrometry (IP-MS) method, we identified two potential podoplanin interacting proteins, i.e. Cofilin 1 and Talin 1 actin binding proteins. The present study reports a role of podoplanin in directing macrophage migration to chlamydial infection site, this suggests a potential for reducing inflammation in chronic chlamydial infected individual by targeting podoplanin.