Reactive lymphadenopathies

Abstract

The human body comprises around 600 lymph nodes as constituents of adecentralized and dispersed immune system. The main task of lymph nodes is cleaning the lymph fluid and defending the organism against outer and inner threats by bacteria, viruses and tumour cells. The histologic picture of lymph nodes reflects the different strategies of the innate and adaptive immune system, which allocates antigen presenting cells, macrophages, B‑ and T‑cell systems and reticulum cells. However, the histological picture, without any additional investigations, usually only allows speculation about the causative agent like toxoplasmosis, other bacteria or viruses. This chapter describes different lymph node reactions in detail in order to obtain abetter understanding of specific immune reactions allowing aprecise diagnosis and areliable distinction from malignant processes. The last issue in particular is one of the main tasks of haematopathology. In addition to these known principles, we try to integrate results obtained with the new method of three-dimensional(3D) microscopy of fixed lymphoid tissue. At first glance, this seems to be unusual. Nevertheless, we try to apply this approach, since 3Dvisualization of morphological details provides distinct cellular details as well as new interpretations of cell-cell interactions and the functions of lymphoid compartments, like germinal centres and T‑zones.