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The Role of Humoral Factors in the Initiation of in Vitro Primary Immune Responses

I. Effects of Deficient Fetal Bovine Serum^1,2,

From the Salk Institute for Biological Studies, P.O. Box 1809, San Diego, California 92112

Abstract

Mouse spleen cells cultured in medium containing deficient fetal bovine serum (deficient medium) do not support primary immune responses to heterologous erythrocyte antigens. A factor, here termed deficient serum restoring factor (DSRF), has been isolated which stimulates primary immune responses in spleen cells cultured in deficient medium. DSRF alone does not stimulate DNA synthesis in mouse spleen cultures. It is required along with the immunogen in the period before the onset of DNA synthesis in the activation of precursors of antibody-forming cells. Deficient medium supports the induction of secondary immune responses by spleen cells which have been primed with antigen in vivo. DSRF does not substitute for thymus-derived cells, adherent cells or allogeneic lymphocytes in the initiation of in vitro immune responses. Unless precursor antibody-forming cells are exposed to DSRF they are not susceptible to the inductive stimulus in deficient medium. The in vitro system utilizing deficient medium appears to distinguish between virgin and experienced precursor antibody-forming cells, and offers a new way of identifying the role of humoral factors in the differentiation of antibody-forming cells.

Footnotes

¹ This work was supported by a Ford Foundation Grant, National Institute of Allergy and Infectious Diseases Research Grant AI05875, and a National Institute of Allergy and Infectious Diseases Training Grant AI00430 to Dr. Melvin Cohn.

² We define here the use of several words. Deficient fetal bovine serum (FBS) refers to serum that does not support a primary immune response against heterologous erythrocytes in mouse spleen cultures (1). Deficient medium refers to Eagle's medium supplemented with 5% deficient FBS. Deficient serum restoring factor (DSRF) refers to the factor purified from JLS-V5 cell supernatants which stimulate immune responses in deficient medium (1) and also induces the growth of bone marrow colonies in semisolid agar medium (3). Normal FBS refers to serum that supports a normal primary immune response in vitro (1) and normal medium to Eagle's medium supplemented with 5% normal FBS. Myeloid cells include granulocytes and macrophages; lymphoid cells refer to bone marrow-derived and thymus-derived lymphocytes (3, 4). Precursors of antibody-forming cells derived as a consequence of immunogenic encounter have been termed experienced.