Abstract
Chemokine receptor 5 (CCR5) binds macrophage inflammatory protein 1alpha (MIP-1alpha), MIP-1beta, RANTES, and members of the monocyte chemotactic protein family and is also a receptor for human immunodeficiency virus (HIV). CCR5 ligands can suppress HIV-1 entry into cells. In humans, homozygous mutations of the ccr5 gene confer resistance to HIV-1 infection. The role of CCR5 in defense against microbial infection is unclear. In this study we examined the innate and adaptive immune responses of CCR5-deficient mice to the intracellular bacterial pathogen Listeria monocytogenes. We found that migration of monocytic cells, formation of L. monocytogenes-containing lesions, and bacterial clearance occurred normally in the spleens and livers of CCR5-deficient animals. Activation of macrophages and dendritic cells during the first 3 days postinfection was normal in the absence of CCR5, as demonstrated by intact expression of inducible nitric oxide synthase (iNOS) and production of the cytokines tumor necrosis factor alpha, gamma interferon, and interleukin-12. Priming of L. monocytogenes-specific CD8 T cells also occured independently of CCR5 expression. Previously immunized, CCR5-deficient animals mounted normal secondary CD8 T-cell responses and cleared bacteria from infected organs similarly to wild-type controls, suggesting that CCR5 is dispensable for migration and activation of memory CD8 T cells. Our data indicate that CCR5-mediated chemotaxis is not required for defense against infection with L. monocytogenes.