[A probable glucidic allotypic pattern carried by the Fab fragment of rabbit IgG (author's transl)].

An allotypic specificity of rabbit immunoglobulins designated as A90 has been studied. The A90 pattern found on the Fab fragment and gamma chain of IgG, is located on the constant region of the Fd fragment of IgG. Aa+ molecules (which carry a specificity of the a series) and Aa- molecules (which lack the a series specificity) isolated from the same serum carry the A90 pattern. A90 distribution in a given serum has been studied in several IgG fractions separated by DEAE cellulose chromatography; the most negatively charged of equally concentrated IgG fractions has ten times more A90 allotypic concentration than positively charged ones. The gene controlling A90 allotypic concentration than positively charged ones. The gene controlling A90 synthesis is not linked to a genes. The percentage of IgG molecules carrying the A90 pattern decreases with the age of the rabbits. Part of the anti-A90 antibodies combine with human IgG (of different subclasses) as well as with sheep and mouse IgG (among which they do not differentiate). The absence of linkage between A90 and a genes suggests that the A90 pattern has a glucidic part. We discuss this hypothesis, comparing some features of the A90 pattern to those of IgG human allotypic pattern for which a glucidic structure has been proposed.