Effect of allogeneic cell interaction on the primary immune response in vitro. Cell types involved in suppression and stimulation of antibody synthesis.

A graft-versus-host (GVH) reaction was induced in F1 hybrid mice by the inoculation of spleen cells from one of the parental strains. One week later the spleen cells from the recipients were cultured during the conditions for obtaining a primary immune response in vitro described by Mishell & Dutton (1967). It was found that the antibody response against the thymus-dependent antigen sheep red cells (SRC), as well as the thymus-independent antigen lipopolysaccharide from Escherichia coli 055:B5 (CPS) was markedly depressed. Spleen cells from mice subjected to a GVH reaction (GVH cells) also inhibited the antibody response of normal cells in vitro. The inhibitory effect of the GVH cells on normal cells was not sensitive to treatment with anti-θ serum, but could be completely abolished by treatment with iron powder, which removes adherent cells. By culturing cells of two different mouse strains together in vitro it was possible to obtain stimulation or inhibition of the antibody response depending on the total cell number per dish. The relation of these results to the phenomenon of antigenic competition is discussed. It is suggested that antigenic competition is caused by a non-specific inhibition of cell proliferation, possibly mediated by a locally acting factor. Both thymus-derived and bone marrow-derived cell lymphocytes are affected by the phenomenon. The cells initially responsible for the inhibition seem to be antigen-activated thymus-derived cells (T-cells), which by secondarily activated cells such as macrophages inhibit other cells. A GVH reaction, which generally leads to antigenic competition may, when less pronounced, cause stimulation of the antibody response.