The role of serum in interleukin 1 production by human monocytes activated by endotoxins and their polysaccharide moieties.

Lipopolysaccharides (LPS) as well as polysaccharide (PS) moieties of Bordetella pertussis and Neisseria meningitidis endotoxins induced in vitro interleukin 1 (IL 1) secretion by human monocytes as evaluated by the co-mitogenic assay on C3H/HeJ thymocytes. Because of the role of serum in the specific binding of endotoxins to monocytes mediated by the polysaccharide region [12], experiments were undertaken to study the effect of serum on IL 1 induction. Although the presence of serum is not necessary for the secretion of IL 1 by monocytes stimulated by LPS or PS, the addition of very small amounts of human serum (0.1-1.6%) to the cultures of human adherent cells potentiated the IL 1 secretion, without modifying the background values. Natural anti-B. pertussis antibodies present in the serum were not responsible for the observed phenomenon. Heating at 56 degrees C for 30 min did not alter the enhancing effect. The data presented suggest that the serum component(s) and the IL 1 inducers (LPS or PS) act in synergism by two different pathways since the two signals can be delivered sequentially.