Inability of immunocompetent thymocytes to produce T-cell growth factor under adenosine deaminase deficiency conditions

Five density-defined subpopulations of rat thymocytes were separated by isopycnic centrifugation on a discontinuous density Ficoll gradient and compared with respect to their response to Con A stimulation under normal and adenosine deaminase (ADA) deficiency conditions. This study shows that (a) immunocompetent (low-density) thymocytes and splenic T lymphocytes produce T-cell growth factor (TCGF) in response to mitogenic stimulation in normal culture conditions, but are unable to synthesize effective TCGF in the presence of an adenosine deaminase inhibitor and excess substrate (ADA deficiency conditions), and (b) high-density immunoincompetent thymocytes proliferate and differentiate into mature T cells in response to Con A if effective exogenous TCGF is added to the culture medium but are unable to do so under ADA deficiency conditions.