The helper cell function of primed T cells. I. Marked amplification of antibody formation by antigen-educated T cells carrying surface Ig 6 h after priming

Inhibition of antisuppression by the acute murine graft-versus-host reaction

Profound suppression of both humoral and cell-mediated immunity is a significant systemic effect of graft-versus-host reactions. Although no complete explanation has been advanced for this immunosuppression suppressor cells have been implicated. The data presented in this paper indicate that acute GVH reactions in (C57BL/6J X A/J) F1-hybrid mice induced by the injection of A/J cells severely disrupts the function of the antisuppressor T-cell pathway at both its induction and effector stages. Results show that within 3 weeks of induction of the reaction, Ly1+-T antisuppressor inducer cells lose their ability to generate the serum factor that mediates antisuppression. This factor is normally taken up by and activates Ly2+ T cells which then inhibit suppressor T-cell function. The data also reveal that Ly2+ T cells collected 2 weeks after induction lose their ability to be activated by the antisuppressor factor produced in normal mice. These cells are thus unable to function as antisuppressor effector cells. The uptake of the antisuppressor factor by Ly2+ T cells depends on the expression of Ia antigens on the surface of these cells. Experiments have shown that these antigens are absent from the surface of T cells derived from mice with GVH reactions. This finding may provide an explanation for the inability of these cells to function as antisuppressor effectors. Antisuppression is an important T-cell pathway that is intimately associated with the regulation of immune function. It is possible that the immunosuppression arising in mice with GVH reactions may stem, in part, from unopposed suppressor T-cell activity that results from widespread interference by the reaction with a pathway that normally inhibits suppressor cell activity.

Macrophage T cell interaction. Induction in vitro of a mediator with potent antisuppressor activity

A simple in vitro method is described for the induction of a potent mediator that interferes with suppressor cell function. The mediator consists of three easily identifiable components, Ig, class II determinants and antigen, that form a unique complex similar to, or identical with, the complexes detected in vivo within 3-6 h after immunization. The formation of the antisuppressor mediator in vitro takes place in two steps: the first involves a macrophage-T cell interaction which generates an 'intermediate complex' containing antigen and class II determinants. In the second step the addition of immunochemically purified IgG from normal mouse serum to the macrophage-T cell supernate generates potent antisuppressor activity, which is assayed by the conversion of suppression to immunity. It is suggested that the IgG interacts with the 'intermediate complex' giving rise to the final complex identical to that found in vivo 6 h after immunization. No activity is detected when IgG is added to a supernate of antigen-fed macrophages in the absence of T cells. Furthermore, the T cell plays an additional important role in the formation of the final complexes since it restricts the source of the IgG that will generate the antisuppressor activity. In other words the antisuppressor function is detected only if the IgG matches the donor of the T cell in the Igh locus. The T cell involved in the formation of the complex is the Ly1+ subpopulation. This method should allow elucidation of the genetic, cellular and molecular mechanisms in the activation of this important T cell pathway.

Surface membrane changes of T cells induced by syngeneic tumour cells. II. T-cell defects induced by small tumour cell inocula or tumour cell antigens

Injection of a large number of tumour cells, like other strong immunogenic challenges, is followed within 6 h by the uptake of cytophilic Ig (probably complexes) by a subpopulation of T cells. This phenomenon, known as the "6-hour T-cell response" is abrogated when small tumour cell inocula (10(2)), or small amounts of a preparation from tumour cells, which contains tumour antigens, are injected prior to the immunogenic challenge Abrogation of the "6-hour T-cell response" resulted in a decrease in specific anti-tumour cell immunity as tested in vitro by measuring growth inhibition (cytostasis). It has also resulted in loss of the amplifying function on antibody formation against sheep erythrocytes, normally detected in a T-B cell co-operative system when T cells are used 6 h after priming with sheep erythrocytes. It is postulated that this T-cell defect may represent a mechanism by which tumour cells, in the early stages of their growth, interfere with inductive stages of the immune response for a sufficient period of time to allow the tumour to grow beyond immune control.

Surface membrane changes of T cells induced by syngeneic tumour cells. I. Formation and uptake of complexes of Ig and tumour antigens by T cells

A large dose of tumour cells (10(7)) from two different tumours produced a significant increase of Ig-bearing spleen cells 6 h after intraperitoneal administration in syngeneic mice, like conventional antigens previously tested. Incubation of normal spleen cells in serum taken 6 h after administration of tumour cells reproduced in vitro the changes observed in the spleen cell population of the serum donors, demonstrating the presence of a cytophilic Ig, which was shown to be taken up by T cells. Serum collected 6 h after tumour cell inoculation contains also a 4S factor which can generate in vitro cytophilic Ig for T cells in the presence of a foreign soluble protein or tumour antigen. Extracts obtained from tumours cells, which were shown to contain tumour antigens, were labelled with 125I and mixed with the 4S factor and normal 7S Ig. Upon fractionation of the mixture, high molecular weight material containing radioactivity and 7S Ig were eluted in the void volume, well ahead of the position of both the tumour cell preparation and the 7S Ig. This material contained Ig cytophilic for splenic T cells and it is likely that it represents cytophilic complexes of Ig and tumour antigens. It is postulated that the cytophilic Ig detected in the serum of animals 6 h after injection of a large number of tumour cells represents cytophilic complexes of Ig and tumour antigens formed through the mediation of a soluble factor.