Identification of four allelic variants of the dog IGHA gene.

Multiple IgA subclasses have been identified in humans, primates and lagomorphs, whereas in mice, cattle and dogs only a single subclass has been identified. The two human subclasses (IgA1 and IgA2) are defined by a difference in the length of the hinge region of the alpha chains between the CH1 and CH2 domains. The single IgA subclass so far identified in dogs has an alpha-chain hinge region with a predicted amino-acid sequence similar to that of the human alpha1 chain. Allelic variants that differ in the coding sequence of the hinge region have been identified in mice and pigs. In order to investigate whether allelic variants are present in dogs, a portion of the IGHA gene from eight individual dogs was cloned and sequenced. Four sequence variants were identified, and these differed in the coding region of their hinge. A major difference between the variants was the presence of a base polymorphism in the splice acceptor site for the second exon, which resulted in shortening of the hinge in two of the variants. Individuals expressed one or two of the variants identified, suggesting they may be heterozygous or homozygous. Further work is required to determine the effect of the variation on the biological activity of dog IgA and any relationship to susceptibility to mucosal disease.