Selective Induction of CD8+ Cytotoxic T Lymphocyte Effector Function by Staphylococcus Enterotoxin B

Upon encounter with its antigenic stimulus, CTL characteristically proliferate, produce cytokines, and lyse the Ag-presenting cell in an attempt to impede further infection. Superantigens are extremely efficient immunostimulatory proteins that promote high levels of proliferation and massive cytokine production in reactive T cells. We compared the activation of murine influenza-specific CD8+ CTL clones stimulated with either influenza peptide or the superantigen staphylococcus enterotoxin B (SEB). We found that influenza peptide/MHC and SEB appeared equally capable of eliciting proliferation and IFN-γ production. However, while influenza peptide/MHC elicited both perforin- and Fas ligand (FasL)/Fas (CD95L/CD95)-mediated cytolytic mechanisms, SEB was unable to trigger perforin-mediated cytolysis or serine esterase release. Examination of intracellular Ca2+ mobilization events revealed that the ability to trigger intracellular Ca2+ flux was not comparable between influenza peptide and SEB. SEB stimulated only a small rise in levels of intracellular Ca2+, at times indistinguishable from background. These findings indicate that the short-term cytolytic potential of superantigen-activated CD8+ CTL clones appears to be restricted to FasL/Fas (CD95L/CD95) mediated cytolysis.

HIV-1 Tat Inhibits Human Natural Killer Cell Function by Blocking L-Type Calcium Channels

Herein we show that functional phenylalkylamine-sensitive L-type calcium channels are expressed by human NK cells and are involved in the killing of tumor targets. Blocking of these channels by phenylalkylamine drugs does not affect effector/target cell binding but inhibits the release of serine esterases responsible for cytotoxicity. Interestingly, treatment of NK cells with HIV-1 Tat, which is known to affect several calcium-mediated events in immune cells, impairs their cytotoxic activity. In addition, Tat inhibits the rise in intracellular free calcium concentration upon cross-linking of the adhesion molecule CD11a, engaged during effector/target cell interaction, and the activation molecule CD16. Exogenous Tat does not influence NK-target cell binding but prevents NK cell degranulation. We propose that the molecular structure(s) on NK cells mediating the inhibitory effects HIV-1 Tat belong to L-type calcium channels, based on three lines of evidence: 1) binding of phenylalkylamine derivatives to these channels is cross-inhibited by Tat; 2) L-type calcium channels from NK cell lysates bind to Tat linked to Sepharose columns; 3) the inhibitory effect of HIV-1 Tat on NK cell function is prevented by the agonist of L-type calcium channels, Bay K 8644. Altogether, these results suggest that exogenous Tat is deeply involved in the impairment of NK cell function during HIV-1 infection.