Structural polymorphism of murine C4 and its linkage to H-2

Heretofore unrecognized structural polymorphism of murine C4(Ss) was demonstrated by using two different techniques: immunofixation electrophoresis and immunofixation isoelectric focusing. By these methods C4 was demonstrated as a broad protein band in freshly bled EDTA-plasma of inbred strains and wild mouse lines. Seven variants of C4(Ss) were identified among a large number of mice tested:C4-v (pI 7.7) exemplified by strain SM/J, C4-B(pI 7.5) exemplified by B10, C4-k (pI 7.3) exemplified by C3H/He, C4-bactrianus (pI 7.2) exemplified by Mus m.bacterianus, C4-d.s(pI 7.0) exemplified by DBA/2 and SJL/J, C4-castaneus (pI 6.6) exemplified by Mus m.castaneus, and C4-NC(pI 6.3) exemplified by NC. F1 hybrid exhibited two C4 bands, each of which corresponds to C4 of a parent. The possibility that the observed polymorphism represents variation of Slp was ruled out because an identical C4 pattern was always observed between male and female mice. The observed structural variation of murine C4 is controlled by a single codominant locus localized within or in the proximity of the S subregion of H-2. This was shown by phenotyping several intra-H-2 recombinant strains and backcross progeny, (B10 X NC)F1 X B10 and (B10 X NC)F1 X NC. An alloantiserum specific for one of the C4 variants (C4-NC) was successfully produced in C3H/He mice by repeated injection of purified C4 of NC mouse. This finding suggests that observed C4 variants or at least some of them represent antigenically distinguishable allotypes of murine C4.