Mitogenic response of marmoset lymphocytes: cytokinetics and identification of responsive cells.

Isotope (tritiated thymidine, [H]Tdr) incorporation into lymphocytes from two marmoset species, New World primates which are haemopoietic chimeras, was studied using peripheral blood lymphocyte (PBL) cultures incubated for 1–5 days with different concentrations of Concanavalin A (Con A), leucoagglutinin (LA), bacterial lipopolysaccharide (LPS) from gram-negative bacteria, rabbit anti-marmoset immunoglobulin (anti-Ig) serum, thymosin or irradiated histoincompatible (xenogeneic) lymphocytes. Only the plant lectins and xenogeneic lymphoid cells stimulated the uptake of [H]Tdr. Lymphocyte enrichment experiments demonstrated that cells responsive to plant lectins and xenoantigens were primarily thymus-derived (T) lymphocytes. Bacterial endotoxin (LPS), however, enhanced the mitogenic response of PBL to Con A when LPS and plant lectin were added together at culture initiation. Thymosin caused either enhancement or suppression of the response to Con A depending on its time of addition relative to lectin stimulation. Addition of thymosin to lymphocyte cultures with Con A or 24 h later caused a decrease in isotope incorporation, while addition of thymosin 48 h later caused a 12–100% increase in [H]Tdr uptake. Lymphocyte chimerism did not influence the mitogenic response since single-born, nonchimeric marmosets responded to plant lectins in a manner similar to marmosets with varying proportions of chimeric blood elements. Cytological analysis of stimulated lymphocytes from heterosexual marmosets revealed the percentage chimerism in the polyclonal mitogenic response and the clonal mixed lymphocyte reaction to be similar.