Sequential analysis of T-cell mediated cytolysis: a brief reminder of some possibly informative markers at the recognition and lethal hit stages

Immune cytolysis viewed as a stimulatory process of the target

Humoral and cellular mechanisms of immune cytolysis, as effected by antibody and complement (Ab + C') or by cytolytic T lymphocytes (CTL), have traditionally been considered the end result of early but terminal membrane damage, in turn causing colloid-osmotic lysis of the target cell. A comprehensive theory explaining and relating known prelytic cellular events to subsequent membrane damage is lacking, nor is there a specific picture as to the role and mode of action of Ca2+, which appears to be involved in both complement- and cell-mediated cytolysis (C'MC and CMC, respectively). Recent studies are in support of the view that both Ab + C' and CTL induce a comparable series of prelytic events, in the TC, initiated by membrane depolarization, which in turn bring about voltage-dependent Ca2+ influx or its intracellular release. Persistent elevation of cytosolic Ca2+ can induce massive stimulation of cellular ATPases (actomyosin, Ca2+) and cause exhaustive depletion of ATP. Consequently, Na+-pumping is slowed down and colloid-osmotic lysis ensues. Hence, in our view, membrane damage in immune cytolysis is the result rather than the cause of intracellular events culminating in lysis.

Cytotoxic T-lymphocytes. How do they function?

The central theme of this work has been the roles of the CTL receptor and of MHC-proteins in CTL recognition and lysis. A major conclusion that may be deduced from the work presented here is that one CTL receptor is responsible for both target cell recognition and lysis. Although their function as recognitive structures is well established, involvement of MHC-proteins in the events that follow recognition has not been investigated in detail. We have proposed that MHC-proteins are molecular mediators whereby CTL receptors transmit signals ultimately leading to lysis of the target cell. I see future work on CTL-mediated lysis proceeding in the following directions: 1. Verification and analysis of the precise role of MHC proteins in CTL recognition and lysis by use of cell and vesicle systems of defined composition and structure. 2. Study of CTL-mediated 'lethal hit' in systems enabling analysis of early events (millisecond level) preceding lysis. 3. Grafting of CTL receptor(s) activity onto naive cells, using liposomes or other vehicles, and 4. Production of idiotypic reagents such as monoclonal antibodies specific for the combining site/effector mechanism of CTL.