C4 Phenotype and Gene Distribution in a Population of Eastern Lombardy (Italy)

The fourth component of complement (C4) is a sl-globulin (mol.wt. 200 KB) that acts in the classical pathway of complement activation. C4 molecules are encoded by two closely linked loci, C4A and C4B, located with the genes for the steroid 21-OHase in the vicinity to the HLA-DR locus, in the MHC on.chromosome 6p. (Campbell et al, 1986).