LECTIN RECEPTORS ON IGA ISOTYPES

It has been shown previously that secretory IgA interacts with the man nose-specific lectin of Escherichia cell. The purpose of the study des cribed here was to evaluate whether the N-linked oligosaccharide chain s of the human IgA isotypes IgA1 and IgA2 differ in lectin receptor ac tivity. A range of plant lectins specific for N-linked oligosaccharide chains were tested for their ability to precipitate IgA1 and IgA2 mye loma proteins, secretory IgA and free secretory component. IgA2 myelom a proteins reacted more strongly than IgA1 with the mannose-specific l ectin ConA, whereas IgA1 myeloma proteins reacted more strongly than I gA2 with two galactose-specific lectins, Ricinus communis agglutinin I and Abrus precatorius ius agglutinin. This suggests that IgA2 possess es a larger proportion of short truncated complex type oligosaccharide chains and/or oligomannose type chains than IgA1. Further, IgA2 react ed more strongly than IgA1 myeloma proteins with Lens culinaris (lenti l) lectin, and Pisum satitivum (pea) lectin, suggesting that IgA2 expo ses more of short, complex type chains fucosylated on the core than Ig A1. The differences demonstrated in receptor activity between IgA1 ari d IgA2 may be important in their interaction with the microbial flora, as well with endogenous lectins, such as phagocyte receptors.