Regulation of the immune response. VIII. Characteristics of antibody-mediated suppression of an in vitro cell-mediated immune response

Fc-signalling in the modulation of immune responses by passive antibody

Passive antibody can both suppress and augment immune responses. Until recently, there was virtual unanimity on the importance of the interaction of the Fc portion of modulating antibody with Fc-receptors (Fc-signalling), especially in experiments involving the suppression by antibody. Experiments reported in the last few years, that do not demonstrate the range of Fc-portion/Fc-receptor influences on the suppression of immune responses by passive antibody, have introduced new uncertainty into this field. The purpose of this paper is to review how the initial controversy on the influence of Fc-signalling in inhibition by passive antibody was resolved. Old and new approaches are suggested that may help in resolving the current uncertainty engendered by recent experimental results that were interpreted to mean that passive suppressive antibody does not utilize the inhibitory FcgammaRIIB receptor. An understanding of the factors that influence negative Fc-signalling is needed in order to optimize clinical therapies whose action depends on the suppressive property of antibody.

Regulation of in vitro cytotoxic T lymphocyte generation. II. Demonstration of noncytotoxic alloantigen-specific suppressor T lymphocytes

Both allospecific suppressor T lymphocytes (TsS) and nonspecific suppressor T lymphocytes (TsN) are activated in alloantigen-stimulated mixed leukocyte cultures (MLC). TsS and TsN can suppress cytotoxic T lymphocyte (CTL) induction upon transfer to fresh (second) MLC stimulated by the same alloantigens as in the first MLC (TsS or TsN) or by third-party alloantigens (TsN only). Evidence that TsS and TsN functions are performed by different T cell sets has been restricted to radioresistance of the former but not the latter. Separation of TsS from CTL has proven even more difficult. Methods are reported here which have allowed in vitro induction and functional separation of TsS from CTL and TsN in a totally allogeneic system. TsS are resistant to combined exposure to pyrilamine, a histamine1 antagonist and local anesthetic, during suppressor cell induction, and to X or gamma irradiation thereafter, while CTL precursors (CTL-P) and TsN are more sensitive to such treatments. This allowed us to use these treatments to generate TsS that are not contaminated with functional CTL, CTL-P or TsN. These data show that TsS regulate CTL induction by interacting with responding cell populations, rather than by cytotoxic depletion of stimulator cells.

Coexistence in human sera of a cell (membrane?) ANTIGEN AND Of autoantibodies directed against it

Antibodies purified from sera of patients with Burkitt's lymphoma by absorption onto and elution from cultured lymphoblastoid cells, were labeled with 125I and repurified by repeating the absorption-elution procedure. The doubly purified antibodies could bound with a high degree of efficiency to immunoadsorbents prepared by entrapping in polyacrylamide gel normal human serum or exudate fluids from patients with ovarian or breast cancer. Binding was specific, as it could be inhibited by high dilutions of human sera but not by animal sera. Globulin fractions of human sera were strongly inhibitory. Their capacity to inhibit was lost after treatment with rabbit anti-human IgG serum, indicating that at least part of the inhibition could be ascribed to antibodies. Some inhibitory activity was also found, however, in the "albumin" fractions of sera, suggesting that an antigen was also involved. It appears, therefore, that practically all human sera contain antibodies reacting with an antigen(s) which is present on human cells and is also circulating freely in serum and other body fluids. Sera of patients with Burkitt's lymphoma contained, on the average higher concentrations of these antibodies, as compared to sera of individuals not suffering from this disease. This antigen is thought to be associated with the cell membrane and has been identified in cells of widely differing origin.

Immunological enhancement of a murine tumor allograft by passive alloantibody IgG and F(ab')2

The F(ab')2 fraction of an anti-tumor IgG alloantiserum induced passive enhancement of tumor allografts in inbred mice about as well as did intact IgG; i.e. apparently the Fc fragment is not required for suppressing cellular immunity. Passive F(ab')2, however, was somewhat less efficient than intact IgG or whole alloantiserum in depressing the allohemagglutinin response. The latter finding is in accord with previous observations on the relative inefficiency of F(ab')2 in feedback inhibition of the humoral response of mice to a heteroantigen.

Interference with antibody-feedback by irradiation, thymus cells, the allogeneic effect, and serum factors

Low doses of irradiation, increased number of T cells, increased T cell activity as in the allogeneic effect, or early activation of an in vitro cell-mediated immune response all confer resistance to antibody feedback. In some of these systems, the resistance is directed against immunosuppression by intact IgG antibody whereas suppression by F(ab')2 antibody is either not changed or increased. These forms of interference with immunosuppression by antibody, are explained in terms of an Fc-dependent model for antibody-feedback regulation.