ABSTRACT
The observations that serum and/or plasma contain an immunoinhibitory factor were first made in 1959 by B. B. Kamrin. This preceded by more than 10 years the observations that cellular elements may also have an immunosuppressive activity. There are different lymphocyte-produced stimulating and suppressor factors and even stimulatory and suppressor substances produced by the macrophage. It is unclear which if any of these substances are present in blood or body fluids in sufficient quantities to produce a significant immunoregulatory activities in these fluids. Humoral immunosuppressive factors have been observed in the serum of cancer patients, in the ascites bathing cancer cells, in the medium bathing tumor cell cultures, and as extracts directly derived from tumors or tumor cells. Although the suppressor activity appears ultimately to reside in a peptide, in untreated samples of the cancer fluids the suppressor activity may be isolated in an a-macroglobulin fraction.
