Moving in for the kill: natural killer cell immunoregulation requires CXCR3

Abstract

Natural killer (NK) cells dictate the pathogenic outcomes of infection via both direct killing of virus-infected cells and indirect immunoregulatory killing of antiviral T cells. The latter involves a perforin-dependent mechanism targeting activated CD4 T cells during the first three days of infection. Given that perforin-dependent killing involves cell-cell contact, we speculated that NK cells must re-locate proximal to recently activated T cells within the white pulp (WP) follicles of secondary lymphoid tissue during this critical temporal window of immunoregulatory activity. As expected, virus infection prompted a gradual accumulation of NK cells within T cell rich regions of splenic WP that peaked by the third day of infection. NK cells deficient in the chemokine receptor CXCR3 exhibited impaired localization to the WP and a markedly diminished capacity to suppress antiviral T-cell and germinal center B-cell responses. Our results reveal a critical role for CXCR3 in properly positioning NK cells to prune developing antiviral T cell responses, which potentially explains loss of tolerance and enhanced immune-mediated organ damage in absence of CXCR3. Strategies to curtail localization of NK cells in the WP during immunization may be an effective means to enhance vaccine-elicited immune responses.