Flow cytometric analysis of CD19⁺lymphocytes in BM from a healthy control and 2 RS-SCID patients withArtemis gene mutations.

(A) Gating on CD19⁺ lymphocytes with exclusion of CD3⁺ T lymphocytes, CD16⁺ NK cells, and CD33⁺ myeloid cells, resulting in a purified “B-cell gate” (upper panels). Within this B-cell gate, expression of cytoplasmic VpreB (CyVpreB), cytoplasmic Igμ (CyIgμ), and surface membrane IgM (SmIgM) can be evaluated (lower panels), showing several subsets in normal BM with most cells in the most mature (Igμ⁺) precursor B-cell stages. (B-C) Patients Artemis-1 and -2 showed a complete arrest at the transition from CyIgμ⁻ pre-B-I cells to CyIgμ⁺ pre-B-II cells. Although no CyIgμ expression was detected, virtually all CD19⁺ precursor B cells were positive for CyVpreB. This is fully in line with the expression of CyVpreB in early precursor B cells.