Synergy among rat T cells in the proliferative response to alloantigen

Graft-vs.-host reactions: mechanisms and contemporary theories

A graft-vs.-host (GvH) reaction can be initiated by injection of immunocompetent lymphocytes into a histoincompatible host that is unable to reject these cells. The reaction is characterized by splenomegaly, hepatomegaly, lymph node atrophy, body weight loss, dermatitis, and diarrhea, often leading to mortality. The onset and severity of the GvH reaction are determined by differences in histocompatibility antigens between the donor and the acceptor, and by the number and nature of the transplanted allogeneic cells. Many different in vivo and in vitro systems have been devised for experimental studies of the GvH reaction. In several of these models, however, different parameters are measured. Furthermore, the conclusions drawn from these investigations sometimes contradict each other. This paper reviews the experimental data, and discusses the mechanisms underlying the GvH reaction.

Immune response in experimentally induced uremia. VII. Uremic thymocytes amplify the response of control lymph node cells to alloantigens

The effect of experimentally induced uremia in the rat on the synergistic response between thymus cells (TC) and lymph node cells (LNC) was examined. It was found that: (1) Uremic TC and LNC interact in a synergistic fashion which is greater than that observed for control cells; (2) The response of uremic LNC to alloantigens is suppressed when compared to the response of control LNC; (3) Uremic TC provide more help to control LNC in their response to alloantigens than do control TC; and (4) Treatment of uremic rats with cortisone acetate (CA) enhances their TC ability to amplify control LNC response to alloantigens. Thus, it appears that, while the response of uremic LNC to alloantigens is markedly suppressed, there are potent amplifier cells present in the thymus of uremic rats which have the ability to act in synergism with control LNC in response to alloantigens. This effect is significantly greater than the synergistic activity of control thymocytes.

The role of the maturation stage of thymocytes on the phytohemagglutinin and concanavalin A responses in thymocyte and lymph node lymphocyte cocultures in guinea pig. Effects of pretreatment of thymocytes with thymosin or levamisole

Guinea pig thymocytes (TH) and lymph node lymphocytes (LNL) synergized optimally in both phytohemagglutinin (PHA) and concanavalin (Con A) responses in mixtures containing 0.3 x 10(6) TH and 0.2 x 10(6) LNL. Using discontinuous albumin gradient centrifugation thymocytes were separated into two subpopulations (F4 and F6) at different stages of maturation. Immature, PHA and Con A unresponsive F6 thymocytes synergized significantly only in the PHA response. More mature, PHA and Con A responsive F4 thymocytes cooperated well in the Con A response, but only a small synergy was observed in the PHA response. Pretreatment of the unfractionated thymocytes with the low concentration (0.05 microgram/ml) of thymosin decreased significantly their capacity to interact with LNL in both PHA and Con A responses. Preincubation of F4 thymocytes with the high concentration (200 microgram/ml) of thymosin increased the synergy in PHA response. All other combinations with thymosin or levamisole and thymocytes were ineffective on the mitogenic responses in the TH and LNL cocultures. Altogether, the results how that the thymocyte populations that induce synergy in PHA, or in (PHA and) Con A responses represent the two subpopulations of thymocytes with different maturation stages. The differential effects of the two concentrations of thymosin on the thymocytes support further the concept that the thymocytes synergizing in responses to both mitogens are more mature than those synergizing only PHA response. Thus, the ability of thymocytes to interact with LNL is dependent on the maturation stage of thymocytes, and can be utilized to study the differentiation of thymocytes.

Different target antigens for T-cell subsets acting synergistically in vivo

After allogenic transplantation of lymphoid cells into immunologically incompetent recipients, a graft-versus-host (GvH) reaction can occur. The original observation that the GvH reaction is mediated by two interacting types of T cell has led to the proposal that T cells must be subdivided into two subpopulations according to life span and migratory properties. These consist of T1 cells, which are short-lived, sessile cells sensitive to adult thymectomy (ATx), and T2 cells, which are long-lived, recirculating cells sensitive to anti-thymocyte serum (ATS). T1-T2 cooperation has also been demonstrated in vitro in murine and rat mixed lymphocyte culture. The question arises as to whether these T-cell subpopulations are activated by different or identical parts of the major histocompatibility complex (MHC). We report here that for optimal development of the anti-host immune response in a murine GvH reaction, T2 cells have to be amplified by T1 cells. The former cells are activated by a set of MHC gene products that are expressed mainly on immunological cells (H-2I-coded antigens), whereas the latter recognize a different set of MHC gene products that are expressed on almost all cells of the mouse (H-2K/D-coded antigens).