We have previously shown that activation of NK cells by poly(I:C) or tumor treatment of mice increases the level of antigen-specific IgG2a (1, 2). We have now assessed the functional relevance of this effect of the innate immune system on the specific immune response. We found that the increased IgG2a significantly augments antibody-dependent cellular cytotoxicity mediated by NK cells both in vivo and in vitro. Furthermore, we show that both IgG3 producing plasma cells induced by T-independent antigens and IgG2a plasma cells induced in the presence of activated NK cells may be just as long-lived as plasma cells induced by T-dependent antigens. These results indicate that if NK cells are activated early in the immune response, before T cells are recruited, they could exert long-lasting effects. (C) 2000 Academic Press.
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