Effects of five proteins secreted by Chlamydia trachomatis on phagocytosis of mouse macrophages and dendritic cells

Objective To analyze the effects of five proteins secreted by Chlamydia trachomatis on the phagocytosis of macrophages and dendritic cells derived from bone marrow cells of C3H/HeJ mice. Methods Glutathione S-transferase (GST)-CT311, GST-GIgA, GST-cHtrA, GST-OmcBc and GST-Pgp3 proteins were prepared through an Escherichia coli prokaryotic expression system and purified by GST MagBeads. Chlamydia membrane protein GST-IncA was also prepared as a control. Proteins of interest were obtained by cleaving off GST-tag with PreScission protease.Macrophages (MΦ) and dendritic cells (DC) were prepared from bone marrow cells of C3H/HeJ mice and pretreated with either 100 μg/ml or 500 μg/ml of the above proteins.LPS was used as a control to testify the specificity of the proteins′ functions.Four hours after pretreatment, fluorescent beads were added to culture media to evaluate the changes in phagocytosis with direct immunofluorescence assay. Results LPS and low concentration (100 μg/ml) of these proteins had no significant influence on the phagocytosis of DC and MΦ, while high concentration (500 μg/ml) of Pgp3, cHtrA and CT311 could significantly promote the phagocytosis of DC and MΦ. Conclusion Pgp3, cHtrA and CT311 can promote the in vitro phagocytosis of DC and MΦ, which may facilitate the in vivo dissemination of Chlamyida trachomatis. Key words: Chlamydia trachomatis; Secretory protein; Macrophage; Dendritic cell; Phagocytosis