Virendra O. Shah

Flow Cytometric Analysis of Normal B Lymphoid Development

Identification of the antigens expressed on marrow B lineage cells can be used to develop a model for the sequential acquisition of cell surface antigens during B lymphocyte development. The data suggest that the surface antigen expression is highly controlled during the development of B cells with the coordinated acquisition of multiple cell surface antigens during the maturational process. The developmental scheme in figure 6 is inferred from the expression of cell surface antigens on single samples. Confirmation of the progression from one stage to the next requires the isolation of a particular stage with subsequent induction to the next stage in-vitro. These data suggest that the development of B lymphoid cells may be discrete rather than continuous. The most immature cells identifiable in the bone marrow express CD34+ as well as HLA-DR. The earliest recognizable B lineage cells (CD19+, bright CD10+) also express CD34+. These cells are smaller by forward light scattering when compared to the cells which express only CD34+ (precursor of myeloid cells). Cells within stage I also express TdT in the nucleus and are proliferating. As the cells progress from stage I to stage II, the B lineage cells lose cell surface CD34 and nuclear TdT. At this time the density of HLA-DR and CD45 increases while the amount of CD10 decreases. These changes occur with no detectable change in cell size as assessed by forward light scattering. HLA-DP is first detected on the cells at this time. The progression of cells from stage II to stage III is marked by the acquisition of CD20, HLA-DQ, and sIgM. The amount of CD45 increases further in the transition between stage II and stage III. The acquisition CD21 and CD22 as well as the loss of CD10 distinguishes stage IV from stage III. Once the cellular composition of normal marrow has been defined, perturbations from homeostasis can be identified. Since marrow is the tissue most sensitive to injury by most antineoplastic chemotherapy and radiotherapy regimens, a means of quantifying the changes from the normal state can provide an assessment of the cytotoxic injury produced in individual patients. By monitoring the return to normal, it may be possible to more precisely individualize therapy for each patient. With a clear understanding of normal hematopoiesis, it should also be possible to identify maturational blocks which occur in hypoplastic marrow states. This may provide a means of identifying the regulatory points for each lineage and provide strategies for overcoming the inhibition of development.(ABSTRACT TRUNCATED AT 400 WORDS)