Multicolor Immunophenotyping: Human Immune System Hematopoiesis

Flow cytometry is a technique for the examination of patterns of protein expression, particularly on the cell surface. Using fluorescent-labeled antibodies that bind with high avidity and specificity to selected antigens, information regarding hematopoietic maturation has been generated. This chapter describes the identification of normal maturational stages of hematopoietic cells in human bone marrow by multiparametric flow cytometry. The normal immunophenotypic patterns of maturation are (1) CD45 and side scatter gating, (2) stem cells and blasts, (3) neutrophilic maturation, (4) monocytic maturation, (5) erythroid maturation, (6) B-cell maturation, and (7) miscellaneous patterns. Hematopoiesis begins with a quiescent stem cell that proliferates under environmental influences giving rise to progeny capable of differentiation along multiple lineages. The maturation of hematopoietic cells is a result of the tightly regulated and sequential expression of genes and gene products. As a result, the derived protein products exhibit predictable and reproducible patterns of expression with maturation that correlate with morphological or functional stages. However, in hematopoietic neoplasms, an increasing variety of specific genetic abnormalities is described, which are either directly or indirectly capable of perturbing these normal patterns of protein expression. Stem cell disorders such as myelodysplastic syndromes serve as an informative model of maturational dysregulation and illustrate the association between genetic and immunophenotypic abnormalities.