beta 2-Microglobulin-like molecules in low vertebrates and invertebrates.

The occurrence of a β2m-microglobulin- (β2m) like molecule in the sera and extracts from several low-vertebrates and invertebrates has been studied by using 3 homologous and 8 heterologous radioimmunoassay systems. Eight of the RIA were based on the principle of competition between “cold” and radiolabeled β2m whereas 3 other RIA examined the capacity of the unknown reagents to impede the binding of β2m to guinea pig or cod spleen cells or to compete with β2m in its interaction with purified AgB antigens. β2m-like molecules were detected in the serum and extracts of the lizard (Anolis carolinesis) and the goldfish (Carassius auratus) but no evidence was found for the presence of such molecules in the extracts made from the newt (Triturus viridescens). The preparations made from the salamander (Necturus maculatus), the African clawed frog (Xenopus laevis), the catfish (Ictalurus punctatus), and the hydra (Hydra littoralis) were positive for β2m only in 10 to 29% of the assay systems. The extracts made from 2 invertebrate species; the earthworm (Lumbricus terrestris) and the crayfish (Cambarus diogenes) proved to be strongly positive for β2m by all assays and criteria. When quantitively diluted they showed typical inhibition curves and when fractioned on a Sephadex G-200 column, 2 out of 4 fractions (Kav range between 0.21 and 0.80) in each of the extracts had a strong β2m-like activity with a capacity to fully (100%) inhibit the interaction between β2m and AgB antigens. The sera from several crayfish and lobsters (Homarus americanus) and the extracts from these lobsters showed significant variability in β2m-like activity, the lobsters sera being the most positive (27% of the assays). An interesting phenomenon, observed mostly with invertebrate reagents but also with reagents from the low vertebrates and in all assays, was an enhancement in the binding of 125l-β2m to its ligand, which reached in some cases up to 50% (−50% inhibition). The significance of these findings is discussed in relation to the evolution of β2m genes and the emergence of Ig and major histocompatibility antigens.