In vitro selection and extended culture of antigen specific T lymphocytes. II. Mechanisms of selection

Functional selection of antigen specific T lymphocytes can be achieved by culturing thymus dependent (T) lymphocytes from immunized guinea pigs on 'monolayers' of antigen pulsed adherent peritoneal exudate cells (PEC) from nonimmune syngeneic donors. Several aspects of the in vitro selection of T lymphocyte rich peritoneal exudate lymphocytes (PEL) were studied. It was shown that irradiated adherent PEC were equivalent to nonirradiated adherent PEC in supporting selection cultures, indicating that the lymphocytes harvested at the end of the selection culture derive from the immune donors of the PEL and not from the nonimmune donor of the adherent PEC. The relative importance of specific adherence and specific proliferation for achieving selection was determined by comparing the degree of selection obtained when nonadherent cells were discarded at 24 hr with that noted when the discard step was omitted. It was found that omitting the discard step markedly diminished the degree of selection. On the other hand, blocking proliferation with specific alloantisera after the discard step did not diminish the degree of selection, although it did diminish the cell yield. Thus, specific adherence to antigen pulsed PEC appeared to be critical in the selection culture procedure. An estimate of the degree of enrichment obtained by the selection culture procedure was obtained by culturing selected cells in an excess of nonprimed PEL, so that auxiliary cells would not be limiting. Under these conditions, it appeared that selected cells were enriched from 4 to 10 fold in antigen responsive cells with respect to the initial cell population.