Phenotypic expression of cells of stationary elements in human lymphoid tissues. A histochemical and immunohistochemical study.
The stationary elements of lymphoid tissues are composed of four types of cells: histiocytes, interdigitating reticulum cells, follicular dendritic cells, and fibroblastic reticulum cells. The phenotypes of these cells were determined with a large panel of monocyte/histiocyte, C3 receptor monoclonal antibodies, and others. Based on the monocyte-marker expression, histiocytes can be separated into two groups: (1) free histiocytes (monocyte-marker positive) and (2) fixed histiocytes (monocyte-marker negative). The former are characterized by the expression of monocyte markers, such as OK M1, Co Mo2, BRL Mol/Mo2, and Leu M3, whereas the latter are not. Interdigitating reticulum cells are localized in the T-cell zone. These cells are characterized by the expression of 1E9, 2H9, and Leu M1. Interdigitating reticulum cells and fixed histiocytes are similar in terms of marker expression and enzyme histochemistry. However, in interdigitating reticulum cells, the Leu M1 antigen is localized on the membrane, in contrast to histiocytes, in which it has a Golgi distribution. Follicular dendritic cells are present in germinal centers and mantle zones. These cells express complement (C3) receptors and several monocyte markers (including OK M1 and Co Mo2). Follicular dendritic cells are capable of trapping antigens onto their membranes. This unique property makes us reluctant to conclude that follicular dendritic cells are related to monocytes. Fibroblastic reticulum cells express BA-1 and alkaline phosphatase, and they form a dendritic network, especially in the T-cell zone. The results of this study demonstrate that immunoperoxidase staining with monoclonal antibodies can reveal the distribution of histiocytes and dendritic/reticulum cells in lymphoid tissues.