The T4 (CD4) subset of T lymphocytes has been subdivided into two major subsets, a suppressor/inducer subset (T4+,2H4+) and a helper subset (T4+,2H4-) on the basis of the differential expression of the L-C/T200 (CD45) antigens. The 2H4 antigen itself comprises at least three distinct polypeptides at 125,200, and 220 X 10(3) Mr, of which the 200 and 220 X 10(3) Mr polypeptides constitute the highest Mr isoforms of a pool of five distinct L-C/T200 antigens. The T4+,2H4+ subset expresses at least four of these isoforms at 180, 190, 200, and 220 X 10(3) on the cell surface, while the T4+,2H4- subset expresses only the 180 and 190 X 10(3) Mr forms. Pulse-chase analysis and endoglycosidase treatment revealed that the 125 X 10(3) Mr chain of the 2H4 antigen is nonglycosylated, while the 200 and 220 X 10(3) polypeptides are structurally related and derived by N- and O-linked glycosylation from two nascent subunits at 150 and 160 X 10(3) Mr. The function of the T4+,2H4+ subset could be blocked only by an antibody reactive with the L-C/T200 isoforms enriched with O-linked oligosaccharides at 200 and 220 X 10(3) Mr.