Human B Lymphocytes: Phenotype, Proliferation, and Differentiation

This chapter focuses on two sets of molecules involved in the proliferation and differentiation of highly purified human B lymphocytes: the molecules secreted or expressed by T cells and other accessory cells and the receptor molecules expressed on B cells. The immune response results from the precisely regulated proliferation and differentiation of individual clones of lymphocytes. The main function of B lymphocytes is to produce immunoglobulins of which nine different isotypes have been isolated in humans. Each of these isotypes displays specific effector functions such as binding to complement components or binding to a multiplicity of Fc receptors, whose engagement results in a wide array of biological activities. The natural history of a B lymphocyte is divided into two major stages. The first stage, called B lymphopoiesis, occurs in the fetal liver and the adult bone marrow. B cells are distinguished by their expression of membrane immunoglobulins that constitute the B cell antigen receptor. The chapter discusses the expression of many of the antigens specific to human B cells during B lymphocyte development as well as their distribution on T lymphocytes and monocytes. B lymphocytes are widely distributed in the body and extremely motile and are able to interact with many other cell types, such as bone marrow stromal cells, T cells, interdigitating dendritic cells, follicular dendritic cells, and endothelial cells. These interactions depend on specific sets of surface molecules.