The role of NK cells in enhancement of IGG2A response and ADCC in early immune responses

When NK cells are activated with poly (I:C) in mice immunized with either a T-dependent or a T-independent antigen, the level of specific IgG2a is enhanced. In order to examine if NK cells activated in other ways can enhance this response, we treated mice with tumor cells. Only mice injected with BCL1-C11, a B cell lymphoma, which is killed by NK cells efficiently and induces them to produce IFN-γ in vitro, responded by producing higher levels of antigen specific IgG2a. Whereas other tumors were non-effective. This increase is independent of T cells because the same results were obtained using CD3-ζ chain knockout mice. To study the possible functional importance of the increased IgG2a production, the ability of the sera to carry out ADCC was examined using TNP-conjugated 70Z/3 tumor cells, which are resistant to NK killing. The results indicate that sera from tumor treated mice can carry out more efficient ADCC against these specific targets than sera from control treated mice. Therefore, activated NK cells may play an important role in certain early immune responses by influencing specific subclasses of antibodies which can lead to more efficient ADCC of targets bearing the immunizing antigen.