Quantitative estimation of serum Ss level: changes upon the development of autoantibodies, environment and acute...

The level of the fourth complement component was quantitated in sera from several inbred strains of mice of various ages. In NZB and NC mice, which are known to produce autoantibodies spontaneously, the level of C4 increased from one month to six months of age, maintained high C4 levels until 10 months but showed a gradual decrease in serum C4 beginning at one year of age. Direct and indirect Coombs' antibodies were detected after 6 months of age in both strain. C4 level in BALB/c and C57BL/6J mice were relatively constant throughout their life span. In order to determine whether or not antigen-antibody complexes induce the elevation of serum C4 level, either rabbit anti-mouse IgG serum or normal rabbit serum was injected intravenously into BALB/c mice. Sera obtained at various times were tested for C3 and C4 by single radial immunodiffusion. The results indicate that the C4 level elevated after the injection of rabbit anti-mouse IgG, but C3 levels did not change after the same treatment. Normal rabbit serum did not induce a detectable change in C3 and C4 level under the conditions used.