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This paper reviews our experiments using mouse cells transfected with human HLA class II sequences to study several aspects of antigen presentation, including: the production and screening of monoclonal antibodies; the roles of different HLA-DR2 class II loci products in presenting an M.Ieprae antigen to T cells; and, using transfectants super-transfected with ICAM-1, the effect of this accessory molecule on the T cell response.

Some of the proteins that are involved in membrane fusion also belong to the so-called AAA-type family of ATPases. Many of these ATPases have accessory molecules, which may act as ‘adaptors’ to mediate the binding of the ATPase to a membrane-bound receptor. Now, rat p97 — an AAA-type ATPase — has been found to have an accessory factor called p47. Moreover, it is the p97/p47 complex, rather than p97 alone, that is required for membrane assembly.

The expression and function of asialo-GM1 (AsGM1) in alloreactive cytotoxic T lymphocytes (CTL) was studied. We have shown previously that the cytotoxic reactions mediated by AsGM1 + -cloned CTL were blocked by anti-AsGM1 or by purified AsGM1. To further determine the role of AsGM1 in CTL-mediated cytotoxicity, we examined the correlation between this blocking effect and the expression of AsGM1 on effector and target cells. Now we found that the blocking by anti-AsGM1 was largely dependent on the expression of AsGM1 on the effector cells in a dose-dependent fashion. The expression of AsGM1 on target cells had only little effect on the blocking of cytotoxic reactions by anti-AsGM1 or AsGM1. A threefold difference was seen in the blocking of AsGM1 + and AsGM1 − targets. The observation was in sharp contrast to the effectors as no blocking was ever seen with AsGM1 − CTL. Similar to CTL effectors, we found that the expression of AsGM1 and L3T4 were mutually excluded on mitogen-activated T cells, despite the fact that they could coexpress in resting T cells. The expression of AsGM1 on CTL effectors was associated with the antigen-nonspecific natural killer (NK)-like or lymphokine-activated killer (LAK)-like activity exerted by the alloreactive CTL. All AsGM1 + CTL possessed LAK activity against antigen-unrelated tumor targets, and the AsGM1 − CTL only displayed antigen-specific alloreactivity. The LAK activity was associated with the expression of AsGM1 on effectors, and was not related to the AsGM1 expression on target cells. These findings indicate that the AsGM1 expressed on alloreactive CTL may function as an accessory molecule for T-cell receptors in the antigen-specific alloreactive cytotoxicity mediated by AsGM1 + CTL. The expression of AsGM1 may also be related to the activation of an NK-like apparatus in these CTL. Therefore, AsGM1 not only may be involved in cytotoxic reactions mediated by AsGM1 + CTL, it may also modulate the specificity of the CTL cytotoxicity.

SUMMARY We review evidence from this laboratory that T cell recognition of Mlsa determinants is not controlled solely by the α-β T cell receptor (TcR) molecule. We propose a model in which Mlsa recognition reflects a receptor-ligand interaction between two sets of complementary accessory molecules, one molecule (Mlsa) being expressed on B cells and the other (the anti-Mlsa receptor) on T cells; this interaction augments recognition of self class II molecules by the TcR. The biological role of Mls molecules might be to facilitate physiological T-B interaction.

Publisher Summary This chapter discusses the diversity and disparities of ouabain sensitivity. The almost universal use of ouabain or other cardiac glycosides to define and measure Na pump-related activities in intact cells and membrane preparations is based on the consistency and potency of its effect. It is widely recognized that large differences in sensitivity to ouabain do exist among various species and, within an organism, among tissues. Ouabain inhibition in most tissues of rats and hamsters requires notoriously high concentrations and is rapidly reversible. In addition, the ouabain dose-response of Na, K-ATPase of rat and hamster kidney membrane preparations fails to show the usual shift to higher concentrations at low temperatures, and the antagonism of ouabain binding by K may also be lacking. Some rodent tissues have been reported to have ouabain sensitivities in the micromolar range even though reversal is rapid in one of these. The ouabain sensitivity of K influx is measured at 37°C at 10 m M K O in erythrocytes of several species of rodents, and ouabain reversibility by measuring fluxes following three rapid washes at 5°C in ouabain-free solution. Low ouabain sensitivity may be a reflection of either a characteristically different Na, K-ATPase, or of an impinging accessory molecule, or both.

The contributions of the CD4 and CD8 accessory molecules to T cell receptor (TCR) specificity and thymic selection are matters of considerable interest. The tight correlation between CD4 expression and class II recognition and CD8 expression and class I recognition suggest that the accessory molecules are involved in specific MHC class recognition (Reinherz et al. 1983; Swain 1983). Supporting this notion is the fact that class I-specific responses can be blocked by anti-CD8 and class II by anti-CD4 antibodies (Marrack et al. 1983; Dialynas et al. 1983a). Others have provided data which demonstrate direct binding between accessory molecules and MHC (Doyle and Strominger, 1987).