The formation of stable E rosettes by human peripheral blood lymphocytes after short exposure to concanavalin A

E rosettes formed by peripheral human T lymphocytes and sheep red blood cells disintegrate readily following prolonged incubation at 37°C. "Stable" E rosettes, resistant to prolonged incubation at 37°C, are formed by "activated" T lymphocytes. In the present study, "stable" E rosettes were found to be formed not only by peripheral blood lymphocytes (PBL) exposed for a prolonged period to concanavalin A (Con A) but also by PBL exposed to Con A for only 1 hr at 37°C. This phenomenon was dose dependent. At the highest concentrations of Con A tested, about 50% of the PBL formed "stable" E rosettes. Con A treatment seemed to exert its effect on T lymphocytes since its activity was highest on T cell-enriched fractions of PBL and lowest on T cell-depleted cell fractions. Moreover, treatment of PBL with specific anti-T serum prevented the induction of "stable" E rosettes by Con A. Treatment of PBL with Con A at 4°C, rather than at 37°C, did not result in the induction of the capacity of forming "stable" E rosettes. Exposure of PBL to sodium azide likewise diminished the induction of stable E rosettes by Con A. Treatment of PBL, either with microtubule depolymerizing agents (colchicine, vinblastine) or with cortisol succinate prior to their exposure to Con A, increased the proportion of PBL forming "stable" E rosettes. These results indicate that Con A induces the formation of "stable" E rosettes by causing a redistribution of cell surface receptors on T lymphocytes, which in turn enhances the interaction of E receptors with sheep red blood cells. Exposure of Con A-treated PBL to α-methyl-mannopyranoside for 30 min at 37°C prevented the mitogenic activity of Con A but did not significantly reduce the proportion of cells forming stable E rosettes. Suspensions of PBL exposed to Con A for various time intervals were separated into fractions capable of forming stable E rosettes and into those lacking this property. No significant difference was found in the mitotic response of these cell populations to an additional Con A stimulus. Thus, the relationship of cell membrane changes, reflected in the formation of stable E rosettes, to the mitotic "triggering" of the cells remains to be elucidated.