Isolation, molecular properties and allotype of mouse C1q

Mouse C1q, a subcomponent of the first component of complement, was purified from mouse EDTA plasma by a combination of precipitation with polyethyleneglycol, affinity chromatography on IgG-Sepharose, ion exchange chromatography and molecular sieving. Mouse C1q was compatible with human C1q in the sense that it shows C1 hemolytic activity by the combination with human C1-r and C1-s. The molecular weight of mouse C1q as estimated by SDS-PAGE was approximately 410,000 and almost the same as that of human C1q. After treatment of mouse C1q with 4 M urea, three distinct subunits were obtained on SDS-PAGE in non-reducing condition. Moreover it was shown that there are small, yet definite differences in the molecular weights of the subunits between the two mouse strains. Three subunits of the C1q from C3H and ICR showed apparent molecular weights of 62,000, 58,000 and 53,000 but those of DDI showed 62,000, 55,000 and 51,000. These results suggested the existence of allotype of mouse C1q, and indeed, alloantisera made by injecting the C1q of ICR to DDI reacted in Ouchterlony double diffusion test with plasma of ICR, C3H, AKR and BALB/c, but not with DDD, DKI, C57BL/10 and C57BL/6.