Apparently non-expressed alleles of factor B (BF) code for hypomorphic proteins

In three families with an apparent non-expressed factor B (BF) allele (BF*Q0), advanced methods of isoelectric focusing for the determination of BF F subtypes revealed different hypomorphic BF products (BF QL) with functional hemolytic activity expressed by the assumed BF*Q0 allele. A Taq I and a Msp I restriction fragment length polymorphism as well as the Ba fragment of the expression products showed banding patterns for the BF*QL alleles corresponding to BF S types, whereas an altered Bb fragment was seen in two BF QL products. In one family an intragenic recombination site within the Bb part of the BF gene was assumed. Investigations of factor B and its conversion fragments, as demonstrated by the used methods, allow to complement molecular genetic investigations of BF*Q0 alleles in heterozygous genotypes on a protein level. We conclude that apparently non-expressed alleles of factor B code for hypomorphic but functionally active proteins.

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.

Prevention of bleomycin-induced fibrosing alveolitis with indomethacin: stereological studies on rat lungs

The prevention of the pulmonary toxicity of bleomycin (BLM) has been investigated in experimental models where pulmonary damage was induced with one intra-tracheal dose of BLM. The present investigation was carried out as a pre-clinical study in which BLM was administered systemically. The non-steroid anti-inflammatory drug indomethacin (INDO) was chosen as a possible candidate for pulmonary protection. Twenty female Wistar rats were treated daily with 4 mg/kg (7.3 units) BLM intra-peritoneally for 50 days and 20 rats with BLM and with 1 mg/kg INDO subcutaneously for 62 days. There were 20 animals as controls. Histological examination revealed fibrosing alveolitis in the BLM-treated group which was markedly suppressed in the combination group. Quantitative morphological (stereological) parameters demonstrate that BLM induced alveolar wall thickening (+45%), pulmonary fibrosis (+110%), and an increase of alveolar wall nuclei and of intra-alveolar macrophages (volume densities +43% and +133%, P less than 0.001). In contrast, after combination with INDO significant differences to the control group could not be detected except for a slight increase of intra-alveolar macrophages (+62%). Thus, INDO is a highly efficient agent in the prevention of BLM-induced pulmonary damage.

Factor B (BF) nomenclature statement

A common nomenclature for factor B (BF) allotypes is recommended as a result of the BF Reference Typing of the VIth Complement Genetics Workshop and Conference, Mainz, FRG, 1989. It has generally been agreed that the alphanumeric BF nomenclature according to Mauff et al. should also be used in the future for all major BF allotypes distinguishable by standard agarose gel electrophoresis (AGE). The common BF F subtypes and further described rarer subtype variants are not detectable by standard AGE. Therefore, the nomenclature had to be extended. For the subtypes of BF F an alphabetical designation with capital letters will now be used: FA and FB. The designation of the five rarer subtype variants was modified after the reference typing to FB1, FB2, SB1, SB2, and SB3. Hyposynthetic variants detected in samples with previously assumed non-expressed (BF*Q0) alleles are now designated as SQL, M1QL, and M2QL, HQL' characterizing their lower concentration.

Factor B reference typing report

In a factor B (BF) Reference Typing of the VIth Complement Genetics Workshop and Conference, Mainz, FRG, 1989, 99 samples from 13 laboratories, including 18 families, were investigated with the majority of presently known typing procedures. Among the major ('standard') allotypes BF SO4 was found to be new. For the group of common BF F subtypes samples from 11 laboratories including complete family data from 5 laboratories were compared. The subtypes BF FA and FB were recognized and confirmed to be identical in the samples from all groups. Within a third group rare subtype variants of F and S were compared and characterized. In samples submitted from individuals with assumed non-expressed (BF*QO) alleles unexpected and hypomorphic gene products were seen. The investigation of DNA samples for restriction fragment length polymorphisms from the same set of individuals revealed a correlation of the Msp I 0.7-kb fragment with BF F, and confirmed the correlation of a Taq I 6.6-kb fragment with BF FA.

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.

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.