Specific and nonspecific NK cell activation during virus infection

The natural killer (NK) cell activation receptor Ly49H is required for resi stance to murine cytomegalovirus (MCMV). We show here that NK cell prolifer ation and production of interferon-gamma (IFN-gamma) was not dependent on L y49H expression during early MCMV infection. During a later phase of infect ion, however, Ly49H(+) NK cells selectively proliferated and this expansion was blocked by anti-Ly49H administration. With vaccinia virus infection, n either the early nor late phase of NK cell proliferation was selective for Ly49H(+) NK cells. These findings indicated that Ly49H(+) NK cells were spe cifically activated by MCMV and that MCMV infection was characterized by no nspecific and specific phases of NK cell activation in vivo.