Inhibitory and activatory receptors for MHC class I molecules

What Is Going on with Natural Killer Cells in HIV Infection?

Natural killer (NK) cells represent 10-15% of circulating lymphocytes and are important mediators of both natural and adaptive immunity. They participate in immune surveillance against malignancies and virus infection and are involved in the complex immune responses of transplantation, autoimmune diseases and immunosuppression. They can also mediate physiological regulation of hematopoiesis, homeostasis of reproduction and placentation. In recent years new advances have been achieved in understanding the mechanisms whereby NK cells exert their cytotoxic and regulatory roles. Here, we review the physiology of NK cells with special attention to its role in HIV infection.

Allogeneic MHC class I ligands and their role in positive and negative regulation of human cytotoxic effector cells

The allogeneic mixed lymphocyte culture (MLC) has served as an important experimental system for elucidating the cellular and molecular basis of human lymphocyte responses. Complex mixtures of lymphocytes are stimulated by disparate alloantigens, inducing cellular activation and generating a cytokine milieu that is an excellent breeding ground for the proliferation and differentiation of many distinct lymphocyte subsets. Cloning of individual lymphocytes following alloactivation has allowed various cytotoxic lymphocytes to be isolated and characterized with respect to phenotype and specificity. These analyses have revealed that all types of cytotoxic effector cells are regulated by interactions with MHC-peptide ligands, however, the consequences of these interactions can result in opposite functional outcomes. In this review we summarize how allogeneic MHC class I-peptide ligands positively or negatively regulate the activities of four distinct groups of cytotoxic lymphocytes and how this information might be transferred into clinical use.