Hereditary subtypic patterns detected in the Ba fragment of complement factor B: Occurrence of four common alleles in Japanese

Abstract

A procedure which can detect subtype-specific minor bands of factor B (BF) by polyacrylamide gel isoelectric focusing is presented. After zymosan-mediated fragmentation of BF in serum via alternative pathway for complement activation, serum samples are subjected to isoelectric focusing in a narrow pH range (4.2-4.9). The Ba fragments are detected by using immunoblotting. In addition to the previously reported minor bands with subtypic specificities, heterogeneities are observed in other minor band group, where a single minor band corresponds exclusively to a subtype in a regular combination with the previously announced subtypic patterns. A one-to-one correspondence of a single band to each subtype provides an unambiguous determination for three subtypic phenotypes deduced from the two divided BF*F alleles, BF*FA and BF*FB. An autosomal codominant heredity is confirmed through segregation analysis. A population survey reveals that four common alleles, BF*S, BF*FA, BF*FB, BF*Fb1, occur in a Japanese population and the former three alleles, except BF*Fb1, occur in a Cambodian population. The presence or absence of a single anodal minor band was found to be the only difference after neuraminidase treatment of FA and FB, implying that an amino acid substitution responsible for the FA-FB subtypic difference is involved in an additional acquisition in FA of an oligosaccharide unit with a charged sialic acid.

A BF subtype “Fb1” is a marker gene of some mongoloid populations

“…IEF has been applied to BF subtyping, revealing the existence of two subtypes in the BF*F allele mainly in Caucasoid populations. We recently developed a new procedure for detecting the FA-FB subtype in the Ba fragment obtained after zymosan treatment (Suzuki et al, 1989). Geserick et al (1989 reported a Fbl-like variant named FB1 detected in a German family and later they have reported that this variant was different from BF*Fbl in Mongoloid at the VIth Complement Genetics Workshop and Conference (Mainz, F.R.G., 1989).…”