Circulating natural antibody quantification. Detection of natural antibody (IgM) specific for (A) phosphorylcholine, (B) chitosan/chitin, and (C) dsDNA (calf thymus DNA) determined (see Materials) from serum of WT, Cr1KO, and Cr1/2KO mice. (n=12–22, 8–16 week old sex matched mice; error bars represent SEM; *=p<0.05, **=p<0.01, ***=p<0.001 by student’s t-test).