Augmentation of marrow growth by thymocytes separated by discontinuous albumin density-gradient centrifugation.

Mouse thymocytes were separated by discontinuous albumin density-gradient centrifugation. The ability of B6 thymocytes from the gradient fractions to increase the number of spleen nodules formed by B6 marrow cells in B6D2F1 recipients was compared with that of similar numbers of B6 thymocytes from an unfractionated cell suspension. Thymocytes from any of the gradient fractions were not more effective than thymocytes from an unfractionated suspension in augmenting marrow-cell growth, indicating that the presumptive 'effective cell type' in this system cannot be separated from the total thymocyte population by its buoyant density properties.