Soluble FcR Block Suppressor T Cell Activity at Low Concentrationin VitroAllowing Isotype-Specific Antibody Production

IgA and IgG binding factors (BF) can be found in the supernatant (Th sup) of cultures containing macrophages and CD4+ T cells stimulated with particulate antigens such as SRBC. Previous work indicated that these IgBF, when mixed with normal serum immunoglobulin, could block the activity of suppressor T cells (Ts) and allow IgA and IgG PFC responses in vitro. We present serologic and functional evidence that IgABF and IgGBF in Th sup are soluble …