The in vitro generation of suppressor lymphocytes involves interactions between PNA+ and PNA- thymocyte populations.

Employing cell fractionation with the aid of peanut agglutinin, it was found that at least two subpopulations of T cells are required for the generation of suppressor T lymphocytes in culture. The co-operation of these two subpopulations, the medullary and the cortical types of thymocytes, is required for the induction phase but it apparently plays no role in the expression of the suppressive effect. With the aid of genetic markers, it was found that in medullary-type, cortisone-resistant, PNA-negative T cell was the progenitor of the suppressor lymphocytes, while the cortical type cells performed an accessory (regulatory?) function. Finally, it was observed that allostimulation of T cells in culture give rise to both 'helper' and suppressor cells. The generation of 'helper' lymphocytes requires allostimulation for less than 24 hr while the induction of suppressor cells requires a longer period of stimulation which leads in the end to predominance of the suppressor effect.