Immunomodulatory effect of serum on lymphocytes—Consequences for the study of immunostimulants in vitro and in vivo

Abstract

The immunoregulatory effect of serum or plasma on the functions of body cells is often overlooked. Plasma is the natural environment for the cells of the immune system for at least a part of their life span and is the supplier of nutrients and regulatory molecules to the lymphoid tissues harboring immunocompetent cells. The plasma or serum immunoregulatory factors affect both in vivo and in vitro testing of immunostimulants. The serum immunoregulatory factors may be grouped into (1) supporting factors, (2) augmenting (co-mitogenic) factors, (3) mitogenic factors, and (4) suppressive factors. Some of them develop physiologically and appear or dissappear during ontogeny, aging, pregnancy and other physiologic changes, others appear in connection with various diseases. The augmenting and mitogenic factors are mostly poorly defined. The natural and disease-induced immunosuppressive factors are a heterogeneous family of molecules ranging from immunoglobulins, through alphaglobulins and lipoproteins up to unidentified molecules of molecular weights from less than 6000 daltons to over 200,000 daltons. Proteins or polypeptides seem to play an important role in natural immunosuppressive factors, polysaccharides in disease-induced immunosuppressive factors. The presence of immunomodulatory plasma or serum factors affects the evaluation of immunostimulants in both in vivo and in vitro testing. All the cells, serum or plasma of experimental animals or donors should be pre-tested and carefully selected when immunostimulants are tested.