[Functional significance of reactive histologic changes in lymph nodes (author's transl)].

Being a reservoir of lymphocytes and plasma cells the lymph nodes are an integral part of the immune system. B and T lymphocytes in the lymph nodes show a distinct topographical distribution. The follicular outer cortex and the medullary cords are predominantly populated by B cells. The paracortical zone between cortex and medulla, is again subdivided in T cell areas and regions with heterogeneous populations of T and B lymphocytes. Even in the normal state nodal lymphocytes maintain a permanent exchange with blood lymphocytes via the mechanism of lymphocyte recirculation. Reactive structural changes of immunologic origin result in an increased immigration of blood lymphocytes into, as well as in local clonal proliferation within the lymph nodes. Four different morphologic patterns of nodal reaction can be determined in terms of functional impact: (1) cortical plasma cell reactions, (2) paracortical plasma cell reactions, (3) germinal center reactions, all three associated with humoral immune responses, and (4) hyperplastic changes of the paracortex associated with cell-mediated immune reactions. In both humoral and cell-mediated immune responses there may be an additional sinus histiocytosis, or mast cell hyperplasia.