Oral immunization of the African clawed frog (Xenopus laevis) upregulates the mucosal immunoglobulin IgX

Abstract

The frog Xenopus laevis is a model species for developmental biology but is also of significant interest to comparative immunologists. Amphibians are the oldest group of organisms in which both the B lymphocytes of some species undergo immunoglobulin (Ig) class switch recombination and also have a dedicated mucosal Ig isotype. The purpose of this study was to test the hypothesis that frog IgX would be produced in response to oral immunization. In order to facilitate studies of humoral, and especially mucosal immunity, in this model species, we developed a gavage technique for oral immunization. The result of this oral administration of antigen to frogs was assayed by the induction of the mucosal antibody isotype, IgX, in plasma by enzyme linked immunosorbant assay (ELISA), and a significant IgX upregulation was detected compared to frogs receiving systemic immunization into the coelom. These data are consistent with the view that IgX is the functional analog of mammalian IgA and mandate further studies of the relationship between IgX and IgA. Additionally, the gavage technique should be adaptable for functional studies of gut-associated immunology in other small aquatic vertebrates.

A cold-blooded view of adaptive immunity

“…As more immunoglobulins were cloned, however, it became clear that IgX is orthologous to IgA, re-estimating the emergence of this isotype to the origins of tetrapods 169 . IgX levels increase after immunization with mucosal antigens 170 . In addition, unlike IgY but similar to mammalian IgA, switching to IgX can occur in the absence of T cells.…”

Mucosal Immunoglobulins

“…For example, antibodies analogous to IgM will undertake these roles in some cases, whereas in others alternative Ig isotypes have evolved such as IgX in amphibians (Du et al, 2012) and IgT in teleost fish (Zhang et al, 2010).…”

Evolution of B Cell Immunity

“…Recently, it was revealed that in contrast to intracoelomic injection, oral immunization of antigen in frogs induces IgX in plasma (59). In contrast, following intraperitoneal immunization with DNP, specific anti-DNP IgM and IgY, but not IgX, were significantly induced in serum (55).…”