Publisher Summary This chapter focuses on the important discovery that virus-specific cytotoxic T cells are dually specific for virus and for a self cell surface antigen encoded by the major histocompatibility complex (MHC). The initial work was carried out on the lymphocytic choriomeningitis virus system but it soon became evident that the same phenomenon applied to many other viruses. In addition, the same principle has been found to hold for other antigenic systems, such as trinitrophenyl coupled to cells, minor histocompatibility antigens, and the H-Y model. Graft rejection and the need for genetically homogeneous inbred mouse strains for cancer research led to the development of transplantation immunology and immunogenetics. The result is that the gene complex coding for major transplantation antigens is one of the better understood mammalian genetic regions. Cytotoxic T-cell specificity is comparable to serological specificity. Because quantification of specificity or cross-reactivity is difficult, and because of the technical limitations of these cytotoxic T-cell assays, results are interpreted with great reservation. MHC restriction reflects the fact that the effector function of T cells is determined by the kind of Self-H recognized together with the foreign antigen on cell surfaces: K and D are receptors for lytic signals, I determinants are receptors for cell differentiation signals that are delivered antigen-specifically by T cells.

MHC-restricted cytotoxic T cells: studies on the biological role of polymorphic major transplantation antigens determining T-cell restriction-specificity, function, and responsiveness.

On analysis ofin vitro assays of human natural killer (NK) cell function the inadequacy of commonly used methods of expressing lytic activity was apparent. A comparison was made of the data obtained using modifications of two equations—the simple exponential fit and the von Krogh equations. Both of these equations were found to satisfy the following essential criteria for use in these assays. First, the majority of the results obtained in the chromium-release assay could be used in data reduction; second, the resultant “dose-response” curve was reduced to linearity; and third, a single numerical expression was obtained which was directly proportional to the cytotoxic activity. Of the two methods the more conventional exponential fit was found to be the simpler to use. The closeness of fit of the experimentally derived data to the ideal curves did not support the possibility that normal lymphocyte preparations contain suppressor cells capable of inhibiting NK activity. Data have also been presented showing that NK-sensitive targets could be categorized with respect to their susceptibility by comparing the slopes of the target cell survival curves obtained using the exponential fit equation. These observations are relevant to the accurate assessment of NK activity in patient populations and to the determination of the effects of disease and its treatment on this activity.

Spontaneous human lymphocyte-mediated cytotoxicity against tumor target cells. IX. The quantitation of natural killer cell activity

Age-associated alterations in human natural killer cells. 1. Increased activity as per conventional and kinetic analysis.

To analyze the critical parameters for effective antiviral cytotoxic T lymphocyte (CTL) activity in vivo, control of lymphocytic choriomeningitis virus (LCMV) infection in the spleen was studied after adoptive transfer of different spleen cell populations into preinfected recipients. The quantitative, qualitative and kinetic requirements for virus control were defined and related to in vitro assays to compare the antiviral protective function of CTL from naive, acutely infected and memory mice. Treatment of mice with an established but limited LCMV infection by adoptive transfer of spleen cells from acutely LCMV-infected mice led to complete virus elimination mainly mediated by donor-derived CD8+ T cell-mediated, perforin-dependent cytotoxicity. Since virus is continuously spreading and the number of infected target cells rapidly increases, the time until target cell lysis is achieved was critical: if release of viral progeny was not prevented early, additional time to perform effector function did not improve overall virus control. When the function of various cell populations was compared in this model, we found that CTL from naive and memory mice perform considerably less well than CTL from acutely infected mice. In vitro studies indicated that this is probably due to the fact that they can not fulfill the limiting time requirements for immediate antiviral protection: while CTL from acutely infected mice can perform lytic effector function immediately, memory CTL require a considerable reactivation time before they can lyse infected target cells. This reactivation does not necessarily involve cell division. These findings illustrate how critical time limitations are for CTL to mediate early control of a dynamic virus infection in vivo.

A functional and kinetic comparison of antiviral effector and memory cytotoxic T lymphocyte populations in vivo and in vitro.

Effect of ascorbate on abnormal neutrophil, platelet and lymphocytic function in a patient with the Chediak-Higashi syndrome.

The mechanism of action of human cytotoxic lymphocytes was studied in two systems: T cell cytotoxicity in cell-mediated lympholysis (CML) and K cell cytotoxicity in antibody-dependent lymphocytotoxicity (ADL). The mechanisms resemble that of an enzyme, if the effector cells are regarded as enzyme and the target cells as substrate. On the basis of a kinetic analysis it was shown that the experimental data are compatible with a simple rate equation, which allows the definition of three constants: p , representing the maximal killing rate of the effector cell suspension (at target →∞); q , representing the maximal lysis of the target cells (at effector →∞); K which represents the Michaelis constant (i.e, the target cell number giving ½ V max ), when extrapolated to effector = 0. The constant K may be taken to reflect the affinity between effector and target cells. Furthermore, for the ADL system the influence of the effector cell concentration on Km was due not to the addition of inert cells but rather to the presence of cells that can bind but not kill. Finally, it was shown that in the ADL a K cell can recycle, i.e., kill more than one target cell. On the basis of these results, experimental conditions are proposed for optimal measurement of cellular cytotoxicity.

W. P. Zeijlemaker

Papers

Cytotoxic activity of human lymphocytes: quanitative analysis of T cell and K cell cytotoxicity, revealing enzyme-like kinetics