Expression of the p75 interleukin 2-binding protein on CD3+4-8-Tac- cells from autoimmune MRL/MP-lpr/lpr mice.

The recently described (Sharon, M. et al., Science 1986. 234:859) interleukin 2 (IL 2)-binding molecule p75 was detected in the CD3+4-8-Tac- "double-negative" cell population selectively expanded in lupus-like autoimmune mice MRL/MP-lpr/lpr using cross-linking studies. Scatchard analysis of the IL 2 binding revealed the existence of approximately 4700 sites per cell with an apparent Kd of 1500 pM. The cell line LD1.T3B, derived from this population, shared surface markers and the p75 presence/p55 absence of IL 2-binding proteins with its in vivo counterpart, displaying around 3100 sites per cell with a Kd of about 1300 pM. Functional studies showed that high doses of IL 2 had an inhibitory effect on the autonomous growth of this cell line in the absence of the development of killer activity. This study provides evidence of the functional abilities of p75, and shows that the use of Tac/p55 surface expression only to evaluate IL 2 receptors and T cell activation can be an oversimplification as well as misleading.