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Biochemical characteristics of the heterophile transplantation antigen (HT-A).

The Heterophile Transplantation Antigen (HT-A) is a clinically important antigen which is found in some human kidneys and on the erythrocytes and in the serum of rats and some other mammals. Recent reports suggest the possibility that the anti-HT-A antibodies responsible for graft rejection may cross react with one or more HL-A specificities. The ideal way to investigate this possibility would be to perform careful serological and biochemical comparisons of purified HT-A and HL-A. We report here the first stage of these investigations, the examination of the biochemical properties of HT-A. The HT-A molecule of rat plasma is apparently a glycoprotein with a molecular weight greater than 1,000,000. The HT-A antigenic determinant site seems to reside in the carbohydrate portion of the glycoprotein. The native HT-A molecule is apparently susceptible to proteolytic enzymes of rat plasma and serum and is cleaved by these enzymes to produce a fragment with a lower apparent molecular weight and a larger fragment which coelutes with lipoproteins during Sepharose CL-4B chromatography. The data presented here should allow development of a rational purification scheme for the HT-A glycoprotein of rat plasma to be used in further studies in the relationship between HT-A and HL-A.