Conditions for the enhancing effect of protease inhibitors on the concanavalin A induced thymidine response of murine lymphocytes

Soybean trypsin inhibitor. An IL-1-like protein?

Soybean trypsin inhibitor (SBTI) shares some structural homology with interleukin-1 (IL-1) and was tested for IL-1 bioactivity. Human T-cells proliferated maximally when stimulated with PMA and SBTI but failed to respond to either stimulus alone. This response was abrogated by neutralizing antibodies to IL-1 beta but not to IL-1 alpha. However, immunoblots showed no cross-reactivity between SBTI and anti-IL-1 antibodies. Furthermore, SBTI did not bind to IL-1 receptors on YT cells and did not activate a murine T-lymphoma or human T-hybridoma. Supernantants from monocytes stimulated with SBTI contained significant levels of IL-1 activity. The data show that SBTI has no direct IL-1 activity but can stimulate T-cells indirectly through an IL-1 dependent mechanism.

The role of dipeptidyl peptidase IV in human T lymphocyte activation. Inhibitors and antibodies against dipeptidyl peptidase IV suppress lymphocyte proliferation and immunoglobulin synthesis in vitro

Dipeptidyl peptidase IV (DP IV), an ectoenzyme in the cell membrane of T lymphocytes, is an important constituent in the process of lymphocyte activation. This conclusion is drawn from the following observations: (a) Proliferation of peripheral blood lymphocytes induced by mitogenic lectins (phytohemagglutinin, concanavalin A, pokeweed mitogen) is suppressed in the presence of DP IV inhibitors. This effect is specific and applies to an irreversible suicide inhibitor as well as to a competitive one in a dose-dependent fashion. (b) Inhibition of DNA synthesis was also induced by a polyclonal anti-DP IV immunoglobulin. (c) As a consequence of impaired T cell function the production of immunoglobulins by pokeweed mitogen-stimulated lymphocytes is also markedly reduced in the presence of DP IV inhibitors.

Involvement of complement in B-cell, T-cell and monocyte/macrophage activation

In the early 70's it had been shown, that for the immune response against T-dependent antigens C3 was necessary, while T-independent antigens, although activating the alternative pathway of complement, triggered antibody formation also in C-deficient mice. During recent years functional and biochemical knowledge about complement binding structures on B-cells and monocytes/macrophages continuously increased and, also, on T-cells C3 binding entities have been detected. In the case of B-cells and, at least in special experimental conditions, in the case of T-cells C3 can exert a proliferative response as long as the cells are prestimulated (excited) by anti-Ig or IL-2, respectively. Monocytes can bind C3b- or iC3b-carrying particles, but only when progressed to macrophages can they phagocytose such particles. Thus the concept evolves that B-cells, T-cells and monocytes can acquire competence for a C3-driven response when excited properly. The involvement of molecules such as CR1, CR2, factor H, IL-2-receptor and others with a basic structure of repeating units of 61 amino acids in the triggering processes is a surprising finding and certainly suggests their functional importance. In the case of T-independent antigens the structures triggering the alternative pathway of complement are the structures triggering monocytes directly. Whether these two functions have a causal relationship has to be shown.

Effect of E-64, thiol protease inhibitor, on the secondary anti-SRBC response in vitro

E-64, L-trans-epoxysuccinyl- leucylamido (4-guanidino) butane, a specific inhibitor of thiol proteases originally isolated from the culture of a fungus, was examined in connection with the immune responses to the splenocytes of mice. In cultures of C3H/He mouse splenocytes, E-64 and its analogues showed mitogenic activity, and some of them enhanced the lymphocyte blast transformation induced by a suboptimal concentration of concanavalin A. E-64 caused a significant suppressive effect on the secondary anti-SRBC responses when 7- or 14-day-primed BDF1 mouse splenocytes were cultured with SRBC, while it induced no effect on cultured splenocytes either from mice treated with cyclophosphamide, from mice sensitized with dinitrophenyl-Ficoll. The results with E-64 and its close analogues revealed that their effects on the immune response roughly correlated with their inhibitory activity against thiol protease. These results suggest that a thiol protease might be involved in the process of secondary immune response in mouse splenocytes.