A natural heterohaemagglutinin in Xenopus laevis serum

In most adult Xenopus laevis the serum contains a 'natural' factor capable of lysing the erythrocytes from a wide variety of amniote species. The factor has no effect on the erythrocytes of another amphibian, Ambystoma mexicanum, nor will serum from one animal lyse red cells from another Xenopus individual. No lysing factor was present in the serum of larval (tadpole) Xenopus. Heating of Xenopus serum to 56 degrees for 30 min, absorption of the serum with zymosan or inulin, or removal of calcium and magnesium ions results in loss of lytic activity, although haemagglutinating activity remains, suggesting that the factor can fix complement. The factor elutes from a gel chromatography column in the 19S peak, and is inactivated by thiol reduction and subsequent alkylation. These findings, coupled with immunoabsorption studies suggest that the haemagglutinin is an immunoglobulin of the IgM class. The significance of this suggestion is discussed in the light of previous reports of 'natural' heterohaemagglutinins in other species.