- The human A33 antigen is a transmembrane glycoprotein and a novel member of the immunoglobulin superfamily. Heath, J.K., White, S.J., Johnstone, C.N., Catimel, B., Simpson, R.J., Moritz, R.L., Tu, G.F., Ji, H., Whitehead, R.H., Groenen, L.C., Scott, A.M., Ritter, G., Cohen, L., Welt, S., Old, L.J., Nice, E.C., Burgess, A.W. Proc. Natl. Acad. Sci. U.S.A. (1997)