Phytohemagglutinin (PHA)-stimulated lymphocytes from peripheral blood (PBL) were used to examine whether T cell xenoantigens are the same or distinct from the receptor for sheep red blood cells (SRBC). An anti-T cell serum (AMT) was directly conjugated with fluorescein, adsorbed to specificity, and used in antibody excess. With resting PBL, AMT stained T cells with a continuous fluorescent ring and completely inhibited spontaneous E rosette formation. When aliquots of the same cells were stimulated with PHA, AMT did not inhibit E rosette formation at concentrations up to 7.5 mg/ml. All T cells incubated with PHA for 24 to 72 hr were double-labeled with SRBC and AMT. Independent modulation of the surface markers was observed on the same cells as evidenced by cap formation with AMT and ringed morulas of SRBC. As controls, B cells purified from PBL or B lymphoblastoid cell lines did not form E rosettes when incubated with PHA. The abrogation of AMT inhibition of E rosette formation upon PHA-stimulated T cells was a time-dependent process requiring 24 hr of PHA incubation. The results indicate that these surface markers unique to human T cells are distinct structural entities, and that the E rosette blocking phenomenon by this xenoantiserum was attributable to steric hindrance.
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