This proposal examines the signalling abnormalities in lpr immature T lymphocytes in order to understand the apparent developmental arrest and refractory state of the accumulating CD3+ CD4-CD8- T cells, and its parallels with normal T cell tolerance. It further studies the possible consequences of the signal defect on the regulation of surface CD4, CD8, and T cell antigen receptor (TCR) gamma/delta, as well as aberrant INFgamma, IL4, and TNFalpha lymphokine profiles produced by lpr immature versus mature T cells. These latter studies may be particularly relevant to the autoimmune process in these mice. The first specific aim completes a study of calcium and phosphoinositide flux in lpr CD4-8- T cells that show transmembrane signal events to be intact. It then uses the information of constitutive CD3 zeta tyrosine phosphorylation and delayed proliferative responses in lpr CD4-8- T cells to explore the temporal expression of two T cell tyrosine kinases, lck and fyn. Finally, the expression of IL2 gene nuclear regulatory proteins by lpr CD4-8- cells are used to further assess discrete signal pathway abnormalities. The second aim examines methylation of the CD8 gene in lpr CD4-8- cells to assess the question of whether these cells underwent thymic selection at a CD4+8+ stage. It will also explore whether the markedly increased levels of TCR gamma and delta mRNA in cultured lpr CD4-8- cells are translated to gamma/delta protein. The third aim examines aberrantly low lymphokine production by lpr immature T cells, in particular, the absence of INFgamma protein despite the presence of INFgamma mRNA. It also explores the aberrantly high levels of INFgamma and possibly IL4 by lpr mature T cells and normal (Pgp-1+) memory T lymphocytes.