Two BF*F subtypes found by isoelectric focusing have restricted distributions in the Finnish MHC haplotypes

The factor B (BF) polymorphism revealed by immunofixation of plasma samples is made up of more than 20 variants, of which 2 variants are common, S and F, 2 less common, F1 and S07, and the rest of the variants are very rare. In this work we have adapted a rapid method to subdivide the BF*F allele into *FA and *FB by IEF in nontoxic agarose gel. The FA subtype manifested as two major bands and FB as one band both in native and desialylated samples. *F1, *S and *S07 were shown as monomorphic proteins, but differ in their sensitivities to degradation caused by neuraminidase treatment. *FA and *FB showed restricted distributions among the HLA haplotypes of the homogenous Caucasoid Finnish population. *FA was positively associated with the haplotypes Cw3,Bw62,C4A3BQ0 (or A3B1) and *FB with the haplotypes A3,Cw4,B35,DR1,C4A3BQ0 (or A2BQ0, A3,2BQ0).