Analysis of lymphoid population in scid mice; detection of a potential B lymphocyte progenitor population present at normal levels in scid mice by three color flow cytometry with B220 and S7.

We have used 3 color FACS analysis (together with dead cell exclusion by propidium iodide) to ascertain the levels of lymphoid lineage cells present in typical young adult (2-5 month) SCID mice. Both mature and early B and T lineage cells are severely decreased (greater than 100X) in thymus, spleen and peritoneum of such mice. Analysis revealed a significant fraction of B220+ cells in bone marrow and, curiously, all such cells co-expressed a determinant recognized by the S7 antibody, likely lost early in B lineage differentiation. Thus, together with B220, expression of S7 may serve to mark the stage at which the SCID defect first becomes manifest, at least in the B lineage. This suggests that B220+/S7+ cells in bone marrow may be pro-B cells or even a lymphoid progenitor population.