Functional characterization of T lymphocytes grown in semisolid agar.

T lymphocyte colony forming cells (TL-CFC) grown in agar in the presence of PHA were assayed for their capacity to induce or suppress polyclonal PWM dependent B lymphocyte differentiation into plasma cells. This was measured by identifying cells containing intracytoplasmatic immunoglobulins by direct immunofluorescence. To validate the helper and suppressor system used in this paper, the inductive capacity of unfractionated T lymphocytes and their subpopulations bearing Fc-receptors for IgM (TM) and for IgG (TG) was measured. The unfractionated T cells and the TM fraction showed helper activity, whereas the TG cells expressed suppressor activity. The TL-CFC grown in agar in the presence of PHA manifested helper activity at low cell concentration. However, increasing the TL-CFC concentration finally caused suppression of B cell differentiation. The suppressor effect could be abolished by prior irradiation of the TL-CFC before seeding them in agar. These results indicate that T cells grown in agar have the functional capacity of T helper and T suppressor cells to induce and suppress polyclonal PWM dependent B lymphocyte differentiation into plasma cells.