Increase by bacterial lipopolysaccharide of antibody production in mice rendered hyporesponsive to lysozyme

The effect of bacterial lipopolysaccharide (LPS) on the immune response of adult mice to hen egg lysozyme (HEL) was studied under conditions in which hyporesponsiveness to HEL was induced by: (i) the intravenous injection of syngeneic spleen cells incubated with HEL; (ii) the intravenous administration of soluble HEL, and (iii) the intraperitoneal injection of HEL in IFA. In all cases, mice were immunized by footpad injection of HEL, with or without LPS. The antibody response produced was measured by the number of indirect anti-HEL plaque forming cells (PFC) detected in popliteal lymph nodes. The incorporation of LPS in the immunizing dose of HEL had little effect on the response of controls; however, it resulted in an appreciable increase in the antibody response of all three groups of hyporesponsive mice. Although, after treatment with LPS, the number of PFC detected in mice made tolerant by spleen cell injection approached those of the controls, lower increases in the antibody response were noted for the remaining two groups of hyporesponsive mice.