Reference typing report for complement component C4

During the 7th Complement Genetics Workshop, Mainz, Germany, May 1998, a co mplement component C4 typing exercise took place with the aim of applying p resent technologies to the definition of reference C4 alleles/phenotypes an d the recognition of nonexpressed (Q0) C4 alleles within expressed haplotyp es. Eleven samples were submitted from 3 laboratories and tested by 14 part icipating laboratories with basic protein-typing technologies; in addition, each laboratory contributed data from local expertise. The samples were in troduced to the reference typing for one or more characteristic allotype or for partial or total nonexpression of one isotype. The blinded samples wer e centrally evaluated and the results discussed among the participants at a plenum meeting. From the results, the samples could be classified into a g roup of common, easy to diagnose pheno-/allotypes, less common but still un animously recognised variants, and a third group with difficult pheno-/allo types. Within the latter group, the allotypes were either new (C4A '92'; C4 B '93') and/or showed partial or total reversed antigenicity and unusual Ro dgers/Chido (Rg/Ch) PCR subtypes (C4A '92'; C4A 12; C4B '35'; C4B '13'). Se miquantitative C4-alpha-chain estimates of relative isotype levels correlat ed well with the number of alleles seen at each locus by agarose gel electr ophoresis, and were superior to other isotype quantitation methods. From th e evaluation of the reference typing it was concluded that the recognition of rare, aberrant or hybrid C4 alleles with partial or total reversed Rg/Ch antigenicity or monoclonal reactivity is still difficult in most instances ; besides isotype dependent lysis, relative migration values, immunoblots w ith Rg- and Ch-specific monoclonal antibodies, Rg/Ch PCR typing, side-by-si de comparison with already described allotypes will ultimately be required. The recognition of nonexpressed alleles within C4A and C4B expressed pheno types remains the major obstacle in C4 genetic typing. Finally, a conclusiv e interpretation of DNA typing results will be achieved only in the context of complete allotyping results at the protein level, and at present cannot replace conventional protein allotyping.