Equilibrium density gradient centrifugation in isotonic gradients of albumin may be used as an analytical tool to reveal features of cell populations not apparent from morphological or size distribution studies. All lymphocyte sources studied gave a complex distribution pattern consisting of many distinct peaks and shoulders.
The thymus contains proportionally more dense lymphocytes than spleen or thoracic duct. The spleen of neonatally thymectomised animals contains proportionally more light lymphocytes than the spleen of normal animals. This suggests density may effect a separation between dense "thymus-derived" and light "bonemarrow-derived lymphocytes.
Normal animals give variation in lymphocyte density distribution profiles from one animal to another. Part of this variation and part of the complexity is attributed to corticosteroid mediated stress effects on the lymphocytes. Corticosteroid injection increases the number of peaks seen in thymus density distribution profiles. Adrenalectomised animals give more reproducible and simpler profiles, although several distinct density peaks remain.
Large lymphocytes are in general less dense than small lymphocytes, probably because of the increased ratio of light cytoplasm to dense nucleus. However, there exists a small proportion of dense, large lymphocytes and light, small lymphocytes. Each given size of lymphocyte showed heterogeneity in its density distribution, in both normal and adrenalectomised animals.
The technique should be useful in a detailed study of the diversity of lymphocytes, of their differentiation and their precise immunological function.