An immunosuppressive factor has been extracted from α globulin containing fractions of human plasma proteins, which we have called “immunoregulatory α globubin” (IRA). Cohn fraction IV has been found to contain this material. The IRA has been assayed by its ability to inhibit human blood lymphocyte proliferation induced in vitro by phytohemagglutinin (PHA). The IRA has been effective in reducing PHA-induced proliferation by 75% at doses as low as 0.2 mg/106 cells in 1 ml of culture. Most fractions, however, were active at 2 to 3 mg/ml. We have also found the IRA to suppress lymphocyte proliferation induced by anti-human thymocyte serum and specific antigens. The concentration of IRA necessary to inhibit these weaker mitogenic stimuli was considerably less than that necessary to inhibit PHA response.

The IRA does not act by cytotoxicity, contains no cortisol and does not appear to interact sterically with the stimulating agents. The IRA is not firmly bound to lymphocytes. In inhibiting the PHA response, IRA behaves as a noncompetitive antagonist of the early metabolic events which lead to “lymphocyte activation.”

This content is only available via PDF.
You do not currently have access to this content.