Toxoplasma gondii, an obligate intracellular parasite, can invade intestinal epithelial cells and elicit a robust Th1 immune response. In this model of intestinal inflammation, CD8⁺ intraepithelial lymphocytes (IELs) secrete transforming growth factor (TGF)-β, which appears necessary for the maintenance of homeostasis in the intestine. However, the mechanism responsible for the IEL migration to the inflamed intestine is still unclear.

An in vitro coculture cell system was used to quantify the IEL attraction by an infected intestinal epithelial cell line (m-IC_cl2). We used CCR5-deficient mice to determine which chemokine receptor—chemokine interaction could be responsible for the recruitment of antigen-specific CD8⁺ IELs to the small intestine for the promotion of parasite clearance and host recovery.

We observed increased expression of several chemokine receptors (CCR1, CCR2, CCR5, CXCR3) in the infected ileum. In particular, CCR5 expression was markedly increased in antigen-primed CD8⁺ IELs. Experiments using recombinant chemokines as well as blocking antibodies showed that macrophage inflammatory protein (MIP)-1α and MIP-1β were critical for their homing. CD8⁺ IELs isolated from CCR5-deficient mice (CCR5−/−), despite their high production of TGF-β and overexpression of activation markers, were impaired in their ability to migrate in vitro to the m-IC_cl2 monolayer or in vivo to the inflamed intestine after adoptive transfer.

Our data emphasize the biologic role of CCR5 as an important component in the migration of intraepithelial CD8⁺ T cells and the regulation of the inflammatory response following parasite infection.