Morphological Evidence of the Interaction Between Plasma Cells and Macrophages in Beagle Dogs

Abstract

The interplay and the close physical contact between lymphocytes and macrophages during the course of immunological reactions involving antigen recognition have been described by many authors. There have been only a few reports, however, on contact between plasma cells and macrophages and these were only in the lymph nodes and spleen of rodents [2, 5, 61 and in people with multiple myeloma [I]. In several independent toxicological experiments in which different substances were used on Beagle dogs over 3 to 9 months, close physical contact between plasma cells and macrophages was found in non-lymphatic organs such as kidneys and mitral valves. Nephropathy induced by K2HP04 [4] was used to show the relationship between such cells. In the kidneys of dogs treated with 0.8 g/kg bodyweight K2HP04 added to the food, different regressive changes in the tubules, a high degree of basement membrane thickening and less frequently mononuclear cellular infiltrates could be shown. Electron microscopically in such areas plasma cell-macrophage complexes occasionally were seen in proximity to the basement membrane of proximal tubules. Generally single plasma cells are encircled by one or more macrophages (fig. I) or cell clusters appear sporadically (fig. 2) in which a macrophage in the center is encased in a rosette of plasma cells. The space between the plasma cells and macrophages is 100 to 200 x lo-' mm (mean 120 x lo-' mm). The intercellular gap was decreased by dot-shaped intracytoplasmic thickenings, especially in the periphery of the plasma cell-macrophage complexes. The plasma cells often had finger-like or pedunculate and mostly plump pseudopods that penetrated the very thick basement membrane of atrophic renal tubules (fig. 2). My findings were distinctive in that the close apposition between the plasma cells and the macrophages in nonlymphatic tissues such as the kidneys and heart valves could be demonstrated. This was frequently found in isolation. An accidental contact, as would be possible in the lymphatic organs [3] which are densely populated with immunocompetent cells seems unlikely. I believe that the plasma cells in the course of their contact with the macrophages carry out immunospecific functions that could arise from an antigen transfer. Evidence for this is the close topographical relationship of the plasma cells to the basement membrane of the atrophied renal tubules. The plasma cells with their finger-like pseudopods penetrate the basement membranes, which form lacunae at these points (fig. 2). As the mature plasma cells doubtless are secretory cells, the possibility should be considered that they secrete particular antibodies directed against basement membrane antigens; this could lead to lysis of the basement membrane.