Tumor-promoting phorbol diesters inhibit in vitro antibody synthesis

The tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate prevents the synthesis of antibodies directed against sheep red blood cells in an in vitro system. The inhibitory effect of 3 phorbol diesters on this immune response was positively correlated with their tumor-promoting activity. The effect did not appear to be mediated through the inhibition of cell proliferation. Results suggest that the tumor promoter may alter the differentiation of the precursor cells to antibody-producing cells.

T cell-produced immunoglobulin binding factor (IBF) bears determinants coded for by the I region of the major histocompatibility complex and lacks allogeneic restriction

An immunoglobulin binding factor (IBF) produced by in vivo alloantigen-activated T cells suppresses in vitro antibody production to sheep red blood cells (SRBC) and probably represents the soluble form of the T cell Fc receptor. To study the relationship between IBF and the major histocompatibility complex (MHC), two types of experiments were undertaken. First, different IBF were prepared by injecting thymocytes from mice of H-2k, H-2b and H-2d haplotypes into irradiated, allogeneic recipient mice. Cells recovered in the spleens five days later were incubated for 2 h at 37 degrees C, and IBF was purified by affinity chromatography on insolubilized IgG. Purified IBF was then applied to immunosorbents prepared with anti-H-2 and anti-Ia anti sera. Acid eluates were then tested for their suppressive activity on in vitro antibody production to SRBC. Under these conditions, IBF was found to react with antisera raised against products of the whole MHC and of the I region of the MHC, but not with anti-H-2 D antisera. These data indicate that IBF bears, or is associated with Ia determinants. Second, IBF preparations from mice of H-2k, H-2b, H-2d haplotypes were tested for their capacity to suppress the in vitro antibody production to SRBC by spleen cells of a series of mouse strains. The data indicate that IBF is not genetically restricted in its function.

Characterization of suppressive immunoglobulin-binding factor (IBF). III. Biochemical and immunochemical characteristics of IBF produced by activated T cells

The biochemical characteristics of immunoglobulin binding factor produced by activated cells (ATC) were investigated. For this purpose, supernatants of ATC were purified by affinity chromatography on insolubilized IgG and the eluted material was iodinated (125I), treated with mercaptoethanol; and run on SDS polyacrylamide gels. The radioactivity was found in two peaks corresponding to m.w. of 38,000 d and 18,000 d. This result extends and confirms our previous findings that IBF produced by ATC is identical to IBF produced by L-5178-Y internally labeled thymoma cells. The effect of various pH, temperatures, and proteolytic and glycolytic enzymes on the binding properties of 3H-leucine-or H-fucose-labeled IBF to IgG and on the polyacrylamide gel profiles was also studied. By all these criteria, IBF appeared to be a glycoprotein in which the presence of the 38,000 to 40,000 d chain is necessary for the binding to IgG. In the attempt to study the relationships between IBF and I-region products, purified IBF produced by ATC was incubated with anti-Ia immunoadsorbent, and the eluted material was iodinated and run on gels. The 38,000 d and 18,000 d chains characteristic of IBF were found to be specifically retained on the relevant immunoadsorbent. These data favor the hypothesis that IBF bears or is associated with Ia determinants.