Subtyping of Factor B by Agarose Gel Electrophoresis. In: Mayr WR, editor. Advances in Forensic Haemogenetics. Berlin: Springer Berlin Heidelberg; 1988. pp. 154-7. [DOI: 10.1007/978-3-642-73330-7_30]

Improvement of BF typing and of BF F subtyping after neuraminidase treatment in the unconverted and converted factor B

When neuraminidase-treated sera are analyzed by agarose gel isoelectric focusing, the factor B (BF) banding pattern is reduced to predominantly one major band without cathodically positioned bands. This not only makes unequivocal typing of BF allotypes possible but also the reliable distinction of all BF F subtype phenotypes with delimitation of "BF F subtype variants". With this new method, serum aging affects the BF determination to a lesser extent than when applying methods that separate native sera. We show that sialylation is not responsible for the BF F subtype polymorphism. All of the investigated BF allotype bands, including those characteristic of the subtypes, show functional hemolytic activity. The banding pattern after removal of neuraminic acid residues ranges from pH 6.8 to 7.3 for factor B, from pH 5.3 to 5.9 for the Ba fragment, and from pH 8.2 to 8.7 for the Bb fragment. The protein structure of factor B is also discussed. Eliminating the superimposition of bands in different BF allotypes, as demonstrated by these methods, proved to be necessary for the detection of hypomorphic BF gene products (BF QL), which are expressed by assumed BF*Q0 alleles in heterozygous genotypes. This allows investigation of BF*Q0 alleles on a protein level, which complements molecular genetic approaches.

The BF F subtypes are detectable in the Ba fragment of factor B

The unanimous recognition of the two subtypes FA and FB of the BF*F allele has repeatedly been challenged. In the present investigation we are reporting about the unequivocal and simple detection of the subtypes on the Ba fragment of factor B by immunofixation isoelectric focusing after conversion with inulin. The common BF phenotypes F, S, and FS could be diagnosed in addition to the subtypes of BF*F which were observed in two regions acidic of the F major band. By comparison of standard phenotypes the subtypes in the Ba fragment corresponded to those of native factor B. All BF bands could be attributed to the Ba fragment by developing Western Blots with monoclonal antibodies directed against Ba. The distribution of the major BF phenotypes and alleles and the BF F subtypes in a population sample of 527 unrelated individuals from F.R.G. was in Hardy-Weinberg equilibrium. The allele frequency was determined to be 0.0731 for BF*FA, and 0.1053 for BF*FB. The advantages of determining the subtypes on the Ba fragment are: broadening of the FA/FB corridor, a more reliable diagnosis of phenotypes, improved distinction between homozygous FA and heterozygous FAFB types, and recognition of common BF phenotypes as well as subtypes in aged sera. It is suggested that the problem in the designation of BF F subtypes by different groups should be resolved by an international reference typing.