Combined immunodeficiency associated with increased apoptosis of lymphocytes and radiosensitivity fibroblasts.

Severe immunodeficiency characterized by lymphopenia was found in two siblings, one of whom was examined in detail. The calcium flux, pattern of tyrosine phosphorylation of proteins, and interleukin 2 (IL-2) production and proliferation in response to mitogens suggested that the peripheral blood T cells activated normally. The peripheral blood T cells were shown to have an activated phenotype with increased expression of CD45RO+ and CD95/Fas. Increased spontaneous apoptosis occurred in unstimulated lymphocyte cultures. The elevated apoptosis was not due to alterations in expression or to mutations in Bcl-2, Bcl-X(L), or Flip, nor could the spontaneous apoptosis be prevented by blocking Fas, suggesting that it was independent of Fas signaling. This is the first inherited combined immunodeficiency associated with impaired lymphocyte survival. Fibroblasts derived from the patient showed appreciable radiosensitivity in clonal assays, but apoptosis was not elevated. Our results show that the fibroblasts represent a new radiosensitive phenotype not associated with cell cycle checkpoint defects, V(D)J recombination defects, or elevated chromosome breakage. We suggest that the affected gene plays a role in an undetermined damage response mechanism that results in elevated spontaneous apoptosis in lymphoid cells and radiosensitivity in fibroblasts.

The protein tyrosine kinase p60c-Src is not implicated in the pathogenesis of the human autosomal recessive form of osteopetrosis: a study of 13 children.

Osteopetrosis has been described in mice generated by homozygous gene disruption of c-src gene encoding for the p60c-Src protein tyrosine kinase (Src-/- mice). The similarities of bone histologic findings in this murine model to those observed in some patients first seen with autosomal recessive osteopetrosis, "malignant" osteopetrosis, led us to investigate the potential role of p60c-Src in the pathogenesis of malignant osteopetrosis in 13 children. In 4 patients a c-src mutation was ruled out by an intragenic microsatellite segregation study. In the other 9 we analyzed p60c-Src expression and function, as well as c-src sequence. The expression was normal in all of the patients tested. In addition, the tyrosine phosphorylation and kinase activity of p60c-Src were also normal in all of the patients. Moreover, in these patients, sequences of the coding region of c-src were identical to the published sequence of the human c-src complementary DNA. These results exclude a role for c-src in the pathogenesis of human malignant osteopetrosis in the 13 patients analyzed.