Cell surface receptors involved in the attachment of murine cytotoxic T lymphocytes to target cells - a study with xenoantisera to T-cell antigens

In previous studies it was demonstrated that rabbit anti-mouse thymus sera (RAT) but not rabbit anti-brain serum (RABR), block the activity of cytotoxic T lymphocytes (CTL). The aim of the present study was to determine to what extent inhibition of the lytic activity of CTL reflects inhibition of the attachment of CTL to target cells. Following heat inactivation RAT and RABR were absorbed with mouse liver and kidney and tested for their capacity to inhibit the attachment of sensitized peritoneal exudate T lymphocytes (PEL) to various target cells. The exposure of sensitized PEL to RABR markedly reduced their capacity to form conjugates with either allogeneic or syngeneic target cells. In contrast, RAT inhibited only the formation of conjugates of sensitized PEL with the respective target cells against which they were immunized. Treatment with RAT had no effect on the formation of conjugates with irrelevant target cells. Additive experiments in which PEL were exposed to a mixture of both RAT and RABR indicated that the two antisera blocked different types of attachment. The inhibitory activity of RAT on conjugate formation could be removed by absorption with B-lymphoma cells but not with myeloma cells. Analysis of the correlation between the inhibitory effect of RAT on cell-mediated lysis (CML) and on conjugate formation revealed that the serum was about twice as effective in its capacity to inhibit CML as to inhibit the attachment of PEL to target cells. The results indicate that while RABR inhibits non-specific attachment of CTL, which does not lead to cell lysis, RAT exerts its effect by interfering with immunologically specific functional receptors on CTL.