Activation of resting T lymphocytes by cross-linked anti-CD3 (T3).

In this study we have examined the role of small numbers of adherent cells in the stimulation of highly purified resting T lymphocytes by cross-linked monoclonal anti-CD3 antibodies (T3). T cells were obtained by 3 cycles of purification, using adherence to plastic surface, nylon wool column separation and rosetting with 2-aminoethyl isothiouronium bromide-treated sheep red blood cells. They were stimulated either with T3 antibodies or with solid-phase rabbit anti-mouse IgG-T3 complexes. In standard high density cultures (1 X 10(5)-2 X 10(5) cells), soluble T3, interleukin (IL) 1 and IL 2, used separately, did not induce proliferation of T cells. Soluble T3 together with IL 2 slightly activated T cells to proliferate. Rabbit anti-mouse IgG-T3 complexes attached to the plastic wells induced stimulation in some cultures. The response was markedly increased after addition of IL 2, but not IL 1. The irregular response of these cultures suggested the presence of another variable signal. When cell numbers were reduced (12 X 10(3) cells), neither cross-linking of the CD3-Ti complex nor addition of exogenous IL 1 or IL 2, alone or in combination, stimulated the T cells to increase DNA synthesis. A positive response, comparable to complete peripheral blood mononuclear cells, was restored with 0.5% supplemented adherent cells, provided that IL 2 was present.