Macromolecular insoluble cold globulin (MICG): A novel protein from mouse lymphocytes—II

Macromolecular insoluble cold globulin (MICG) is synthesized selectively by mouse T-cells. In support of this conclusion is evidence derived from mitogenic stimulation of thymic and splenic lymphocytes. PHA and Con A stimulated a disproportionately large increase in MICG compared to total protein synthesis in spleen and thymus cells, while IgM synthesis in spleen cells only rose parallel with the increase in total protein synthesis. In LPS-treated spleen cells, MICG synthesis rose only in proportion to total protein. Therefore, selective enhancement of MICG synthesis, i.e. as a proportion of total protein synthesis, only occurred under conditions where T-cells were activated. In the presence of complement, antibody to MICG was cytotoxic to virtually all thymocytes and half of the spleen cells. Furthermore, antibody to MICG eliminated the mitogenic effect of PHA and Con A on spleen cells, while the response of these lymphocytes to LPS was normal. Cytotoxicity with antibody and complement also caused a significant diminution of MICG synthesis in spleen cells. Finally, isolated T-cells demonstrated a significant amount of MICG synthesis, while only a trace of MICG synthesis was atrributable to B-cells.