Peroxidase-positive mononuclear leukocytes as possible precursors of human dendritic reticulum cells.

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Abstract
In this report, we provide evidence that suggests the dendritic reticulum cells (DRC) occurring in germinal centers of lymphatic follicles originate from a distinct endogenous peroxidase-positive mononuclear blood cell subset. The new monoclonal antibody Ki-M4 showed a highly restricted reactivity, tested by immune histochemistry, being confined to DRC, lining cells of lymph node sinuses, and to 0.001% of nonadherent mononuclear blood cells separated at a density of 1.077 g/ml; the latter exhibited endogenous peroxidase activity in cytoplasmic granules. Such granules being specific for myelomonocytic cells implies that DRC may derive from a committed nonadherent subpopulation of this cell line, which in turn originates from bone marrow. The Ki-M4-reactive antigen was found to be destroyed by the majority of fixatives and to resist 4% paraformaldehyde for 10 min and cold acetone for 30 sec. In cell suspensions from human tonsils, Ki-M4 showed strong reactivity with the outer surface of DRC plasma membrane. This observation demonstrates the possibility of using Ki-M4 to separate DRC from cell suspensions in functional tests.