Antibody responses of human lymphocytes in vitro. Specificity and physical properties of plaque-forming cell precursors.

When human tonsillar lymphocytes are cultured with pokeweed mitogen they generate a larger number of antibody-secreting cells. A substantial number of the plaque-forming cells generated have specificity for sheep erythrocytes but very few are specific for either bovine or horse erythrocytes. We have investigated the physical properties of sheep erythrocyte-specific precursors and have found that they have the characteristics of larger lymphocytes and are heterogeneous with respect to density. Our results support the concept that the percursors which can be induced by pokeweed mitogen to develop into plaque-forming cells belong to a pre-activated sub-population of lymphocytes.