Effect of immune sera upon enhanced in vitro antibody responses

Immunization of rabbits with S marcescens bacteria in Freund's incomplete adjuvant resulted in development of anti-Serratia sera with bacterial agglutinating properties as well as LPS modulating properties. The antisera reacted with the LPS in counterimmunoelectrophoretic assays. Such antisera also stimulated the LPS induced enhancement of specific anti-SRBC responses from normal spleen cell cultures but did not further enhance the stimulated responses of similar cultures incubated with the smaller molecular weight PS-rich derivative. The antisera had no effect on LPS or PS enhanced nonspecific background anti-SRBC response as compared to normal rabbit serum-treated controls. These results point to a possible role for immune complexes as an enhancer of the immunostimulating activities of LPS antibody-treated cultures and also indicate a difference between LPS and PS as immunomodulators.