A chemokine-to-cytokine-to-chemokine cascade critical in antiviral defense

Macrophage inflammatory protein 1 alpha (MIP-1 alpha) promotes natural killer (NK) cell inflammation in livers during murine cytomegalovirus (MCMV) infections, and NK cell-produced interferon gamma (IFN-gamma) contributes to defense against MCMV infections. A specific role for local NK cell IFN-gamma production, however, has not been established. The importance of MIP-1 alpha and NK cell-produced IFN-gamma in shaping endogenous immune responses and defense in different compartments was examined. MIP-1 alpha deficiency profoundly decreased resistance to MCMV and was associated with dramatically reduced NK cell accumulation and IFN-gamma production in liver. MIP-1 alpha-independent IFN-gamma responses were observed in serum and spleen, and infection-induced elevations in blood NK cell populations occurred in absence of the factor, but peak Liver expression of another chemokine, the monokine induced by IFN-gamma (Mig), depended upon presence of MIP-1 alpha, NK cells, and IFN-gamma. The Mig response was also important for viral resistance. Thus, serum cytokine responses are insufficient; MIP-la is critical for NK cell migration and IFN-gamma delivery to mediate protection; and Mig induction in tissues is a downstream protective response resulting from the process. These results define a critical chemokine-to-cytokine-to-chemokine cascade required for defense during a viral infection establishing itself in tissues.