The spontaneous shedding of the lymphocyte receptor for sheep red blood cells

Cells in vitro constantly synthesize and shed macromolecules into the surrounding culture medium. B and T lymphocytes also synthesize and shed membrane components. The human T lymphocyte is identified by its ability to attach spontaneously to sheep erythrocytes. This binding is more stable at 4 degrees C and is diminished at 37 degrees C, suggesting that the receptor for sheep erythrocyte may be spontaneously shed at 37 degrees C. Therefore supernatants were obtained from human lymphoyctes at 37 degrees C and then added to sheep erythrocytes at room temperature. After washing, these sheep erythrocytes were unable to rosette with human lymphocytes. The potency of the rosette blocking activity in the supernatant was (a) highest when lymphocytes wereincuated at 37 degrees C, less at room temperature, and least at 4 degrees C, (b) increased by increasing the numbers of lymphocytes held at 37 degrees C, (c) disappeared at dilutions of the supernatants greater than 1:8, (d) was completely adsorbed by sheep erythrocytes. This suggests that lymphocytes spontaneously shed receptors for sheep erythrocytes at 37 degrees C.