Key points are not available for this paper at this time.
A complement-dependent bactericidal factor, Ra-reactive factor, that acts specifically on Ra chemotype strains of Salmonella was found in sera of eighteen strains of nonimmune mice, including a thymusless strain. The specificity of binding of this factor to the cells of Ra chemotype bacteria was evidenced by absorption studies. The factor was inactivated by treatment with 0.02 M 2-mercaptoethanol or heating for 30 min at 55 degrees C. This factor was present in mice reared by feeding with a chemically defined, antigen-free diet under germ-free conditions. Fetal and newborn mice from a conventional or germ-free mother had the factor, although the titer was lower than the adults'. The titer in the newborn mice reached adult level 1 wk after birth. The titer in the adult mice did not increase markedly after immunization with heat-killed bacteria or administration of Freund's complete adjuvant and turpentine. These results indicate that this factor is actively produced by mice that have never been stimulated with exogenous Ra antigen.
Kawakami et al. (1982) studied this question.