Elevated natural killer cytotoxicity in HLA-B8 and HLA-DR3-positive individuals

Natural killer and lymphokine-activated killer activity in HLA-B8,DR3-positive subjects

The haplotype HLA-B8,DR3 is over-represented in several autoimmune diseases, implying that genes predisposing people to these disorders are linked to this haplotype. In these diseases, various dysfunctions reflecting an impairment of the immune system have been found. Several reports indicate also that in HLA-B8,DR3-positive healthy subjects similar disorders may be demonstrated. In the present work, we have evaluated NK and LAK activity in these subjects. The study has been performed on monocyte-depleted peripheral blood MNCs by using, the K-562 cell line as a target for NK activity and the HL-60 cell line for as a target LAK activity. LAK cells were obtained by incubating MNCs for 3 days with 100 U/ml of rIL-2. The results of our experiments demonstrate that NK cell activity is significantly decreased in healthy subjects bearing the HLA-B8,DR3 haplotype. Since the number of circulating CD16+ cells is not significantly different between HLA-B8,DR3-positive subjects and negative ones, it is unlikely that this defect is due to a decreased number of NK cells in effector cell preparations. The observation that the treatment with rIL-2 can restore the killer activity of MNCs from these subjects suggests instead that the reduced NK activity may be due at least in part to the imbalance of cytokine network that has been demonstrated in HLA-B8,DR3-positive subjects. Finally, since a decreased NK activity has been reported in the autoimmune diseases linked to this haplotype, our results support the suggestion that immunologic changes observed in autoimmune diseases reflect systemic regulatory disorders that have a genetic basis.

Biology of natural killer cells

Studies of cytotoxicity by human lymphocytes revealed not only that both allogeneic and syngeneic tumor cells were lysed in a non-MHC-restricted fashion, but also that lymphocytes from normal donors were often cytotoxic. Lymphocytes from any healthy donor, as well as peripheral blood and spleen lymphocytes from several experimental animals, in the absence of known or deliberate sensitization, were found to be spontaneously cytotoxic in vitro for some normal fresh cells, most cultured cell lines, immature hematopoietic cells, and tumor cells. This type of nonadaptive, non-MHC-restricted cellmediated cytotoxicity was defined as “natural” cytotoxicity, and the effector cells mediating natural cytotoxicity were functionally defined as natural killer (NK) cells. The existence of NK cells has prompted a reinterpretation of both the studies of specific cytotoxicity against spontaneous human tumors and the theory of immune surveillance, at least in its most restrictive interpretation. Unlike cytotoxic T cells, NK cells cannot be demonstrated to have clonally distributed specificity, restriction for MHC products at the target cell surface, or immunological memory. NK cells cannot yet be formally assigned to a single lineage based on the definitive identification of a stem cell, a distinct anatomical location of maturation, or unique genotypic rearrangements.