Age-Dependent Role for CCR5 in Antiviral Host Defense against Herpes Simplex Virus Type 2

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Abstract
Elimination of viral infections is dependent on rapid recruitment and activation of leukocytes with antiviral activities to infected areas. Chemokines constitute a class of cytokines that have regulatory effects on leukocyte migration and activity. In this study we have studied the role of CC chemokine receptor 1 (CCR1) and CCR5 in host defense during a generalized herpes simplex virus type 2 (HSV-2) infection. Whereas both 4- and 8-week-old CCR1−/− mice resembled wild-type mice (C57BL/6) with respect to defense against the infection, significantly higher virus titers were seen in the livers and brains of 4-week-old CCR5−/− mice. At the age of 8 weeks, CCR5−/− were indistinguishable from wild-type mice and cleared the infection from liver and spleen. Although 4-week-old CCR5−/− mice were able to recruit natural killer (NK) cells to the site of infection, these cells had reduced cytotoxic activity compared to NK cells from wild-type mice. This was not due to lower production of alpha/beta interferon or interleukin-12, two well-described activators of cytotoxic activity in NK cells. We also noted that the spleens of young CCR5−/− mice did not increase in size during infection as did the spleens of wild-type and CCR1−/− mice. This observation was accompanied by impaired proliferation of CCR5−/− splenocytes (SCs) ex vivo. Moreover, migration of CD8+ T cells to the liver in response to infection was impaired in CCR5−/− mice, and adoptive transfer of SCs from CCR5−/− mice infected for 6 days into newly infected wild-type mice did not improve antiviral activity in the liver, in contrast to what was seen in mice receiving immune SCs from wild-type mice. Altogether, this study shows that CCR5 plays an age-dependent role in host defense against HSV-2 by supporting both the innate and adaptive immune response.