Complete arrest from pro- to pre-B cells in a case of B cell-negative severe combined immunodeficiency (SCID) without recombinase activating gene (RAG) mutations

The B-cell lineage in a patient with B-cell-negative severe combined immuno deficiency (SCID) was analysed by using antisurrogate light chain (SL) MoAb s. Peripheral CD3(+) T cells and CD19(+) B cells were absent in the patient . The common gamma (gammac) chain was expressed normally on the patient's p eripheral NK cells and his peripheral mononuclear cells did not possess any mutations in recombinase activating gene (RAG)-1, 2. Normal levels of expr ession of Ku70 and Ku80 protein were found by Western blot analysis. The pa tient did, however, display an increase in fibroblast sensitivity to irradi ation. Furthermore, flow cytometric analyses of bone marrow cells showed th at surface IgM and cytoplasmic mu positive cells were absent and that CD19( +) B cells were composed of only CD34(+) terminal deoxynucleotidyl transfer ase (TdT)(+) SL+ pro-B cells. The complete arrest of pro- to pre-B cell dev elopment in the SCID patient's bone marrow suggests that some genes involve d in V(D)J recombination, excepting the RAG gene, may play a causative role in the immunodeficiency.