In vitro induction of specific immune responses in the absence of serum: requirement for nonspecific T or B cell mitogens.

Abstract

AbstractA mixed lymphocyte culture reaction (MLC) between histoincompatible mouse lymphocytes could be induced in the absence of serum in vitro. There was a steady increase of DNA synthesis for 7 days in the absence of serum, whereas peak activity occurred on day 4 in the presence of serum. Analogous results were obtained when the secondary responses to SRC were determined by stimulation of DNA synthesis.It was not possible to induce a primary humoral antibody response to SRC in the absence of serum. However, if the serum‐free cultures were supplemented with optimal concentrations of T (concanavalin A) or B (lipopolysaccharide, LPS) cell mitogens, a primary specific antibody response to sheep red cells (SRC) could be induced and increased in magnitude for 4 days in culture. Also, a MLC reaction permitted the induction of primary antibody responses to SRC. In the presence of fetal calf serum (FCS), optimal concentrations of T cell mitogens, as well as a MLC reaction, suppressed the induction of a primary antibody response to SRC, whereas suboptimal doses of the mitogen stimulated it.It was possible to induce specific secondary IgM and IgG antibody responses to SRC in the absence of serum.In contrast to the findings with SRC, a primary – as well as secondary – antibody response could be induced to LPS, which is a relatively thymus‐independent antigen.Taken together the results suggest that:a) FCS is necessary for the induction of primary antibody responses, because it contains B and possibly T cell mitogens.b) Primary antibody responses to SRC can be induced in the absence of FCS if nonspecific B cell activation is provided by the addition of either B cell mitogens or B cell activating factors, obtained by activating T cells by specific mitogens or by a MLC reaction.c) Secondary responses to T cell‐dependent antigens are possible in the absence of FCS because of the large number of specifically activated T cells present in the culture system.d) Primary antibody responses to LPS are possible in the absence of FCS because LPS by itself is a B cell mitogen.