Proliferation and differentiation of alloselective NK cells after alloimmunization - Evidence for an adaptive NK response

We have previously demonstrated the activation of NK cells exhibiting RT1 a llele-specific cytolytic activity following intraperitoneal immunization of certain rat strains with allogeneic cells. In the present study, we show t hat the NR allocytolytic activity in BN (RT1(n)) rats immunized with WF (RT 1(u)) cells was associated with an increased proportion of peritoneal, as w ell as splenic, NK cells. Furthermore, the proliferation of NK cells was su bstantially increased in BN (RT1(n)) rats immunized with WF (RT1(u)) cells when compared to that in naive BN rats. In addition, the NK subpopulation e xhibiting the allocytolytic activity in alloimmunized rats exhibited a decr eased expression of the NKR-P1 and L-selectin molecules, but an increased e xpression of the LFA-1 molecule when compared to NK cells from naive rats. Thus, we have shown that the existence of peritoneal NK cells, exhibiting s elective allocytolytic activity in alloimmunized rats, is probably due to a combination of RT1 allele-selective recruitment, proliferation, and the di fferentiation of NK cells. Therefore, in the same way that we regard T cell s as being capable of adapting the immune response, this study presents evi dence for the hypothesis that the specific cytolytic response of alloreacti ve NK cells should also be regarded as adaptive. (C) 1999 Academic Press.