[Proposed practical classification of weak B phenotypes B 3, Bx, B el].

Although the first weak B phenotypes have been observed some thirty years ago, very few comparative studies have been done until now. In this work, different samples were analysed, using immunogenetic methods, thermodynamics, agglutination kinetics and agglutination profiles. Almost hundred weak B samples were tested, belonging to twenty nine families including cis AB but exclusing acquired B and Bh. Using these methods it could be evidenced that the reactive structures differ from one family to another, but are strictly the same within one family. Consequently, each sample should have been called from the family mane; from a practical point of view, it was but necessary to agree on a simple classification. The simplest criteria were looked for such as agglutination velocity on a tile, agglutination picture, presence or absence of anti-B in serum... Three groups were then distinguished: 1) B3, for which the agglutination velocity is high (less than or equal to 30 inches), giving a typical mixed field agglutination pattern; there is no anti-B in the serum; 2) Bx, for which the agglutination velocity is low (larger than or equal to 30 inches), giving generally a weak agglutination pattern; there is a weak anti-B in serum; 3) Bel, for which there is no agglutination at all; the presence of B antigen on the membrane being evidenced by a fixation-elution test; in these three conditions genetic studies proved the phenotype being due to an allele at the ABO locus, the Bel class is the most "discutable"; when an important secretion of B substance can be evidenced in saliva, and the phenotype is proved to be inherited as a dominant character, the appellation Bm can be proposed. On the contrary, when genetics suggest the presence of a modifying gene, the Bel mod or By appellation can be used, according as the type of modification is dominant or recessive. Only one sample appeared to be unclassable, for which the fixation-elution test is positive, but only 5 to 10% of the red cells are agglutinated, giving a dual population pattern; the galactosyl-transferase activity seems to be normal, as well as the--delta H (20.000 cal/mol.). The B weak appellation appears to be the most appropriate for this given sample. This case expected, the proposed practical classification appears to fit well the studied phenotypes. As the various studies on weak B phenotypes, reported in the literature have not been compared within a same laboratory, using the same technics, it appears illusive to apply the proposed classification to the different reported samples. Several already published samples form a part of the present study, but their appellation do not correspond to the previous one; stricklingly, only few B3 (new appellation) have been described in the literature, which let one think that they might be undetected using classical grouping tests, and thus considered as normal B. Of course, there is not an absolute correspondance between the criteria defining A3, Ax, Ael phenotypes and those proposed here for B3, Bx, Bel...