THE REACTION OF IMMUNOLOGICALLY ACTIVATED LYMPHOID CELLS AGAINST HOMOLOGOUS LYMPHOID CELLS AGAINST HOMOLOGOUS TARGET TISSUE CELLS IN VITRO

Non-cytotoxic functions of CD8 T cells: “repentance of a serial killer”

Cytotoxic CD8 T cells (CTLs) are classically described as the “serial killers” of the immune system, where they play a pivotal role in protective immunity against a wide spectrum of pathogens and tumors. Ironically, they are critical drivers of transplant rejection and autoimmune diseases, a scenario very similar to the famous novel “The strange case of Dr. Jekyll and Mr. Hyde”. Until recently, it has not been well-appreciated whether CTLs can also acquire non-cytotoxic functions in health and disease. Several investigations into this question revealed their non-cytotoxic functions through interactions with various immune and non-immune cells. In this review, we will establish a new classification for CD8 T cell functions including cytotoxic and non-cytotoxic. Further, we will discuss this novel concept and speculate on how these functions could contribute to homeostasis of the immune system as well as immunological responses in transplantation, cancer, and autoimmune diseases.

QUANTITATIVE STUDIES ON THE BEHAVIOR OF SENSITIZED LYMPHOCYTES IN VITRO : I. RELATIONSHIP OF THE DEGREE OF DESTRUCTION OF HOMOLOGOUS TARGET CELLS TO THE NUMBER OF LYMPHOCYTES AND TO THE TIME OF CONTACT IN CULTURE AND CONSIDERATION OF THE EFFECTS OF ISOIMMUNE SERUM

When lymphoid cells, derived from rats immunized with respect to homologous skin, were cultured with target cells originally of donor origin, cytocidal and cytostatic activities of the attacking lymphocytes became evident. By application of a sensitive and reproducible quantitative assay system, various aspects of the mechanism of this destructive interaction between target cells and lymphocytes were examined with the following results. 1. The degree of survival of target cells was inversely related to the number of sensitized lymphocytes. Graphic plots of the data indicated that this relationship was an exponential one similar to "single-hit" inactivation phenomena. One interpretation which could be placed on these results is that a single lymphocyte, if immunologically active, was sufficient to destroy or at least have a detectably adverse effect on one target cell. Furthermore, from such a model it could be computed that, of the lymphocytes derived from an immunized animal, approximately 1 to 2 per cent of the cells were immunologically active; i.e., capable of demonstrable destructive activities against homologous target cells in vitro. 2. Morphological studies on the effect of sensitized lymphoid cells on homologous target cells, aftervarious lengths of time in culture, showed that by 7 hours of incubation, the attacking lymphocytes firmly adhered to the target cells. The cytotoxic effect of these lymphocytes generally occurred after the 20th hour. Quantitative studies supported this conclusion; the latent period, i.e., the time required for detectable degrees of target cell destruction to occur, was approximately 20 hours. 3. A consequence of the incubation of target cells with normal lymphoid cells or even with small numbers of sensitized lymphoid cells was an increase in the rate of division of the target cells. As might be expected, this was reflected in a shorter doubling time of these cells. 4. Extracts prepared from sonically disrupted sensitized lymphocytes proved to be no more deleterious to target cells than similar preparations from normal lymphoid cells. Furthermore, no evidence could be obtained that sensitized lymphoid cells, separated from target cells by a Millipore membrane, were cytocidally effective. These data indicated that if a cell-bound substance is involved in the destruction of homologous cells, either it is not toxic by itself, or it cannot be detached from the sensitized cells. In any case, close apposition of the lymphocytes to the target cells is apparently required for the destruction of the latter in vitro. 5. Serum obtained from immunized animals, if heat-inactivated, did not adversely affect homologous target cells; if employed fresh, slight degrees of toxicity resulted. Specific isoimmune sera did not impart any detectable degrees of immunological reactivity upon otherwise normal lymphoid cells. Immune sera, even in high concentrations, did not augment the effect of sensitized lymphoid cells upon homologous target cells; rather a slight inhibitory effect of these sera was detected. 6. Attempts to detect the presence of complement activity, which might have been provided by the lymphoid cells in culture, were unsuccessful. On the basis of these results, it was suggested that the destruction of homologous target cells by sensitized lymphoid cells occurs as a two step process. First, the attacking lymphocytes attach to their targets via a non-toxic cell-bound substance having an immunologic specificity, and then, destruction of the target cells follows the result of some process dependent on the metabolic activity of the attacking lymphoid cells.

ANTAGONISTIC EFFECTS OF HUMORAL ISOANTIBODIES ON THE IN VITRO CYTOTOXICITY OF IMMUNE LYMPHOID CELLS

The ability of specifically immunized lymphoid cells to kill H-2 incompatible target tumor cells in tissue culture was shown to depend on the source of the lymphoid tissue (spleen versus lymph nodes). Marked cytotoxic effects were obtained with regional lymph node cells 7 to 10 days after primary immunization, whereas spleen cells from the same animals had little or no effect. Hyperimmunization did not decrease the cytotoxic efficiency of lymph node cells. Experiments were performed to test the possibility that the weak effect of spleen cells is a result of humoral antibody production, antagonizing the cell-bound immunity. Humoral antibodies were cytotoxic in vitro in the presence of complement only. Their effect was manifested after 2 hours, whereas immune lymph node cells did not require complement and cytotoxicity was not expressed until 24 to 48 hours' incubation. Tumor cell cultures treated with specific humoral antibodies in the absence of complement became resistant to the cytotoxic effect of subsequently added immune lymph node cells, while no such protection was seen when normal serum was added. Thus, humoral antibodies led to an "efferent" inhibition of cell-bound immunity in vitro, in analogy with previous results in vivo.

INVASION AND DESTRUCTION OF HOMOLOGOUS KIDNEY BY LOCALLY INOCULATED LYMPHOID CELLS

When lymphoid cell suspensions from the spleen, lymph nodes, blood, and thoracic duct of parental strain adult rats were injected beneath the renal capsule of F₁ hybrid hosts, the transferred cells and/or their progeny invaded the underlying renal cortex and destroyed most of the tubules which they surrounded. The immunogenetic conditions under which this reaction was observed defined it as a graft vs. host reaction (GVHR). On the 7th day the GVHRs were histologically similar to primary renal homografts undergoing rejection. Lymphoid cells from donors tolerant to the other parental strain were inactive after transfer to the hybrid, whereas cells from either normal or sensitized donors consistently produced reactions of about equal severity. Lewis lymphoma cells displayed malignant, invasive activity but did not destroy either isologous or homologous tissue, showing that the presence of an infiltrate was not per se sufficient to damage the parenchyma. These observations indicate that the GVHRs were manifestations of the ability of the transferred lymphocytes to enter into a homograft reaction with consequent destruction of renal parenchyma, and support the hypothesis that at least some of the lymphocytes which are seen infiltrating primary homografts are the agents which effect their destruction.

Partial tolerant state against H-2 disparate cells. No impaired specific reactivity in MLC, GVH, or antibody production

Injection of CBA mice with H-2-compatible lymphoid cells from C3H hybrids induces a specific reduction of the mixed lymphocyte culture (MLC) response of their lymphoytes. This is not the case after injection of H-2-disparate C3H-hybrid cells, presumably because they are rapidly eliminated due to the immune response of the host. This investigation shows that CBA mice injected with CBA X C57Bl cells (H-2-disparate) at an age of 0-3 days, but not older, develop a specifically reduced MLC response after infusion of C3H X C57Bl cells as adults, indicating that they were tolerant to the C57Bl-determined antigens. However, lymphocytes from such mice showed a normal reactivity against C57Bl as assessed by MLC, graft-versus-host tests, and capacity to produce specific antibodies.

Observations in vitro regarding the mechanism of the cell destruction by stimulated lymphocytes

In contrast to other cells stimulated lymphocytes release substances probably cytotoxic which are incorporated by the target cells. The cellular material is released by tearing off parts of fine processes which the lymphocytes extend on to the surface of the target cells. This explains the before mentioned observations that the cell destruction mediated by lymphocytes depends absolutely on a close contact between the lymphocytes and the target cells.

Increased lymphocyte ATP-ase activity in patients with carcinomas of the oral cavity and larynx

Increased mitochondrial ATP-ase activity was found in circulating lymphocytes from 5 out of 8 patients with carcinoma of the oral cavity or oropharynx and from 5 out of 10 patients with carcinoma of the larynx. In a majority of these cases changes in the ATP-ase activity after treatment paralled to the clinical result of treatment. It is suggested that determination of ATP-ase activity of circulating lymphocytes is of diagnostic value in patients with oral, oropharyngeal and laryngeal carcinomas as well as prognostic value after treatment of the patients.

Specifically decreased MLC response of lymphocytes from CBA mice injected with cells from the H-2-compatible, M-antigen-incompatible strain C3H. Lack of such effect after injection of H-2-disparate C3H-hybrid cells

The mixed lymphocyte culture (MLC) response of lymphocytes from CBA mice against C3H cells was studied after injection of spleen cells from C3H mice or C3H hybrids. Intravenous infusion of C3H cells resulted in a strongly suppressed specific MLC response, but this was not the case when cells from H-2-incompatible hybrids of C3H mice were injected. However, when mixtures of cells from the two parental strains--C3H cells and H-2-incompatible cells--were injected into CBA mice, there was a strongly suppressed MLC response to C3H cells. Mice that were hybrids between CBA and an H-2-disparate strain showed a depressed MLC response against C3H after injection of cells from hybrids between C3H and the same H-2-disparate strain. The results may indicate that a suppression of the MLC response to the strongly stimulatory non-H-2 antigen on C3H lymphocytes develops only when the immunizing cells can survive in the host for long periods, thus exhausting the pool of specifically responsive cells. The presence of another foreign transplantation antigen, such as H-2, on the same cells shortens the survival of the cells in the recipient.

In vitro generation of memory lymphocytes reactive to transplantation antigens

The in vitro generation of memory cells reactive to transplantation antigens is described. Blast cells, obtained from rat lymphocytes sensitized on xenogeneic or allogeneic fibroblast monolayers, reverted to secondary small lymphocytes after transfer from the foreign sensitizing to syngeneic monolayers. These secondary small lymphocytes had a limited in vitro life span of 4-6 wk. They manifested properties of memory cells: upon re-exposure to fibroblasts of the sensitizing phenotype, the secondary lymphocytes adhered to the fibroblast monolayer and transformed into blast cells with cytotoxic activity. The response of secondary lymphocytes was rapid, compared to that of normal lymphocytes, and directed specifically against the primary sensitizing antigens.

Rejection of ascites tumor allografts. II. A pathway for cell-mediated tumor destruction in vitro by peritoneal exudate lymphoid cells

A pathway for cell-mediated tumor destruction in vitro by immune peritoneal exudate lymphoid cells has been proposed. The union of lymphocytes and tumor cells precedes the formation of an intermediate phase leading to lysis. The initial interaction is only partially temperature dependent. The cytolytic process per se is highly temperature dependent, being negligible at 25 degrees C but proceeding rapidly at 37 degrees C. (51)Cr release from tumor cells is demonstrable within 10 min at 37 degrees C and can be reversibly arrested by cooling. Once initiated, lysis is largely independent of additional interactions and continues at almost full rate for 30 min. The effector cells are not lysed and appear to be free to enter into further effector cycles.