The BF locus and HLA: Rare alleles coding for functionally active and inactive factor-B products

The genetic polymorphism of properdin factor B(BF) was studied in different populations. The rarer alleles, BF^*F1 and BF^*S1, occurred in Caucasians, were less frequent in North American blacks, and were not demonstrated in any of there Oriented populations studied. Two further alleles of BF, termed BF^*FM and BF^*SM, were found to exist in these populations. The BF^*FM allele, which was found only in Caucasian, codes for a functionally inactive factor-B product, whereas the BF^*SM allele (found in a single Chinese individual), like other alleles of BF, codes for a functionally active product. HLA haplotype analyses in individuals carrying the rarer alleles of BF revealed not only a strong association between B^*F1 and HLA-B18 and BF^*S1 and HLA-Bw50 but an even stronger association between these BF alleles and alleles of the two C4 loci. BF^*F1 occurred most frequently on a C4A^*3,B^*Q0 haplotype, ubreas the BF^*S1 allele was usually found on a C4a^*2,B^*1/B^*Q0 haplotype. HLA haploypes carrying the BF^*FM and BF^*SM alleles all carried the more common C^*4A3,B^*1 haplotype.