Normal Blood and Bone Marrow Populations

It is essential to have a sound understanding of the nature and immunophenotypic characteristics of the normal cell populations encountered in bone marrow and peripheral blood. It is also important to have some understanding of lymphoid cellular interactions in the normal lymph node and thymus. This process is necessary if we are to understand the origin of the myeloid and lymphoid neoplasms encountered in routine diagnostic immunophenotyping and helps us understand why certain neoplasms carry a particular repertoire of antigens. It not only helps in the diagnosis of neoplastic disorders but equally gives support to the recognition of reactive phenomena. The populations of cells which inhabit the bone marrow are constantly changing throughout the life of a normal individual. When this environment is challenged by infection, drugs, intercurrent medical disease and, of course, primary haematological disease, the populations change or can respond and react in a variety of ways. We need to be aware of these reactions such that we do not over or under interpret the findings. This chapter is set out as a framework or foundation of normal myeloid and lymphoid ontogeny. Our understanding of this process is still incomplete but we can only safely recognize abnormal situations once we are fully familiar with the normal resting blood and bone marrow cellular environment.