Subtyping of factor B by agarose gel electrophoresis

Assays for complement proteins encoded in the class III region of human MHC

Investigation of the complement proteins encoded in the class III region of the human MHC isclinically significant. A low level of components that make up the classical pathway is indicative of an underlying in vivo complement activation or primer complement deficiency. Hemolytic tests of C4 and C2 described are the only methods that allow quantitification of the functional complement proteins. The application of these sensitive techniques is unavoidable if inactive complement proteins are present. The complex hemolytic titration process protocol described in detail makes possible the use of this test. Assays to determine complement components belonging to the MHC III region were completed by a basic phenotyping test of the standard factor B alleles. This simple technique is a very useful first-step assay for clinical laboratories engaged in genetic studies.

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

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

A factor B subtype, BF*Fb1, was first detected in Japanese by using isoelectric focusing or agarose gel electrophoresis in Tris/glycine/Veronal buffer. Our previous studies suggested that BF*Fb1 may be characteristic of some of Mongoloid populations. To investigate further distribution of BF*Fb1, samples randomly collected from Japanese in Yonaguni island of Japan and Cambodian were tested. BF*Fb1 was not observed in a Cambodian population whereas in a Japanese population of Yonaguni island, BF*Fb1 occurred at a frequency five times as high as those in main islands of Japan. In paternity cases, a Korean family with three offsprings was shown to transmit BF*Fb1 from the accused man to one of the offsprings. These data strongly indicate that BF*Fb1 is a marker gene for some of Mongoloid populations.

Human BF*F-subtypes: segregation analysis with inclusion of MHC haplotypes

The segregation of factor B(BF)F subtypes was analyzed in conjunction with other MHC markers in 15 families with 89 offspring. Informative data for BF F subtypes were obtained from 11 families, 6 of them with known recombinant individuals for the HLA-B/DR/GLO region. The subtypes did not contribute further to the localization of the cross-overs, but followed the known segregation of conventional BF allotypes. In 2 families of one kinship, the recognition of heterozygous BF*FAFB individuals could be established following the inclusion of three generations. The rarer of the two BF F subtype alleles, BF*FA, is positively associated with the HLA haplotypes BW62, CW3, C4A*3 and A29, CWX, B44, C4A*3, B*1, DR7. BF F subtypes are regarded as a very useful additional tool for studies of MHC organization and disease association.

Heterogeneous nature of human complement factor B: an electrophoretic approach for the analysis of its oligosaccharide chain structure and its physiological breakdown products

Factor B is a glycoprotein which plays an essential role in the alternative pathway of complement activation. It carries the proteolytic activity of the convertases, and its physiological breakdown products Ba and Bb have some effects on the cells of the immune system. Human factor B exhibits a microheterogeneity and five isoforms are present in serum. The nature and origin of the microheterogeneity was investigated by using electrophoretic techniques. Treatments of factor B with neuraminidase and glycopeptidase F show that this microheterogeneity is mainly due to differences in its sialic acid content, varying from seven to eleven residues per molecule, and resulting in different oligosaccharide structures. However, deglycosylated factor B reveals a residual, nonallotypic variation in the Bb region of the polypeptide backbone. We confirm the presence of four asparagine-linked oligosaccharide chains of the complex type in native factor B, two of which are located in the Ba fragment, and the two others in the Bb fragment. The prevalent isoform of the native protein carries two sialic acid residues per oligosaccharide chain. Biosynthesis experiments show that the microheterogeneity of secreted factor B from HepG2 cells is acquired during the processing of its glycans. However, in vitro-secreted factor B is more heterogeneous than the serum protein. We propose a structural model for the microheterogeneity of the native protein and its physiological fragments. We discuss as well the feasibility of electrophoretic techniques to deal with microheterogeneity analysis.

Factor B (BF) subtyping by isoelectric focusing: methods, nomenclatures, genetics and forensic application

Usually factor B (BF) typing is performed by means of the traditional agarose gel electrophoresis. Using isoelectric focusing, the system can be extended by two common subtypes of BF F. The existence of BF F subtypes has in the meantime been confirmed by various authors and in different populations. Their inheritance has been proven by family- and mother/child analyses and molecular-genetic studies (correlation with restriction fragment length polymorphism). Different typing methods as well as different nomenclatures seem to indicate that the subtypes FA and FB (according to Geserick et al.) are identical with the Fb and Fa subtypes (according to Teng and Tan). At present, some confusion still exists for the less frequent variants and subtypes which possibly could be identified by direct comparison of the patterns. The BF system is a valuable marker in paternity testing. Its chance for exclusion of paternity in Caucasian populations has been calculated to be about 14% for agarose gel electrophoresis and increases to about 16% for BF F subtyping by isoelectric focusing. Preliminary results indicate that BF may also be used for typing of bloodstains (up to 2 weeks old).