Factor B subtyping in sera and bloodstains by isoelectric focusing and immunoblotting

The polymorphism of BF was investigated in 765 unrelated Japanese individuals by isoelectric focusing and immunoblotting. Besides five common subtypes three rare variants were observed. The allele frequencies were: BF*S = 0.8078, BF*FA = 0.1797, BF*FB = 0.0105, BF*Var. = 0.0020. The above method was successfully applied to subtyping BF in stored bloodstains. The determination limits were: at 4 degrees C 8 weeks, at room temperature 2 weeks and at 37 degrees C only 2 days after storage. The BF subtyping is of practical use in medicolegal individualization of unknown bloodstains.