Immunological Relationships of Serum α-Macroglobulins in the Human,Rat,and Rabbit 1

Summary

Rabbit serum contains two immunologically distinct α-macroglobulins, α₁M and α₂M, while only an α₂M has been described in human serum. Rat serum contains an α₂M which, like rabbit α₁M, increases in acute inflammation. Antisera to these macroglobulins cross-react with serum proteins in different species. Using such antisera, we have shown: (i) rabbit α₁M corresponds to human α₂M and to a normal protein in the rat; (ii) the α₂M that appears in rat serum in relatively large amounts during acute inflammation is antigenically related, but not identical, to a protein present in normal rats, which is homologous to rabbit α₁M and to human α₂M; (iii) rabbit α₂M is antigenically related to a protein in the rat which does not increase during acute inflammation; (iv) rabbit α₂M has no homologue in human serum that has as yet been identified.