Pretreatment of murine thymocytes by phytohemagglutinin inhibits the binding of H-concanavalin A.

The binding of H-concanavalin A (Con A) to cortisone-resistant and normal mouse thymocytes, which greatly differ in mitogenic responsiveness, was compared. Almost equal numbers of 3H-Con A molecules (7 x 10(5) molecules per cell) were found to bind to both cell types, and the rates of H-Con A binding were nearly identical. The binding capacity of thymocytes for H-Con A decreased rapidly after removal from the thymus and incubation in protein free synthetic medium. Similarly, mitogenic responsiveness droped rapidly after cells were exposed to this medium. H-Con A molecules bound to cells were dissociated from them after a brief incubation, about 30 percent of radioactivity being lost in 2 hr with increasing radioactivity being found in the supernatant. When cells were pretreated with PHA-P, which is a T cell mitogen, their mitogenic responsiveness to Con A was suppressed along with H-Con A binding to the cells. In contrast, a B cell mitrogen, LPS, that has a synergistic effect on the Con A mitogenic response in thymocytes had no effect on binding of H-Con A to thymocytes.