Activation and enhanced contact of human T-lymphocytes with autologous red blood cells are required for their stable adherence at 37 degrees.

The adherence of human red blood cells (RBC) to autologous T-cells does not occur in the body, and in vitro is elicited at 4 degrees. Autologous E-rosetting at 37 degrees has not previously been described. In this work, lymphocyte-RBC adherence has been studied in mixed leukocyte-RBC cultures and in whole blood from healthy donors. Vital, cytochemical and electron microscopic studies have shown that T-cells may form stable E-rosettes with autologous RBC at 37 degrees. As in the previously reported cold-dependent reversible rosetting, stable rosetting is mediated by the erythrocyte LFA3 and lymphocyte CD2 molecules. Uniquely, this phenomenon requires both T-cell activation and an enhanced contact between the T-cell and RBC membranes. These requirements were met by exposure of cell cultures to: (1) PHAE, the erythroagglutinating component of PHAP, or (2) to either non-erythroagglutinating mitogens, PHAL, Con A, OKT3 or SEA, or to antigens of typhus group rickettsiae or salmonellae, provided that the RBC membrane was desialyted. Cultures derived from individuals seropositive to rickettsiae or vaccinated with salmonellae demonstrated the adherence phenomenon after antigen exposure when neuraminidase was present in the culture medium. The system 2 described here can be used as a diagnostic tool for defining activated T-cells and T-cell clones with the memory to antigens capable of inducing cell-mediated immunity.