Pathology of non-Hodgkin's and Hodgkin's lymphomas

Non-Hodgkin lymphomas (NHLs) are neoplasms that arise from lymphocytes of either B- or T-cell lineage or rarely from histiocytes. The anatomic location and many of the biologic features of various NHL types can be related to their normal counterparts. Normal B-cells are concentrated in the follicles and medullary cords of lymph nodes and in the follicles of the spleen [1]. The lymphoid follicles represent the proliferative site of the B-cell system. Upon antigen stimulation, secondary germinal centers develop in which rapid cell division of B-cells takes place. The medullary cord region of the lymph node represents the secretory component of the B-cell system. By contrast, T-cells are selectively concentrated in the paracortical regions of lymph nodes and within the periarterial lymphoid sheaths of the spleen. In addition, small numbers of T-cells are found within follicles where they help in the induction of B-cell differentiation [2, 3]. Histiocytes are preferentially found in the subcapsular and medullary sinuses of lymph nodes and the cords of Billroth in the splenic red pulp. Histiocytes are also a part of the reticuloendothelial system of the liver and lung. Tissue histiocytes have two broad categories of function. Most histiocytes are phagocytic, whereas a minority of specialized cells is involved in antigen processing and presentation to B- and T-cells [4].