'Morphology of immune lymphocytes in homograft lymph'

An improved method for the demonstration of fibrin in biopsies of rabbit skin homografts

Tissues embedded in resin are convenient for routine use when the presence or absence of fibrin in them is to be confirmed using the electron microscope. To visualize fibrin using the light microscope, sections (1.0-2.0 micron) from such specimens should be stained with Methylene Blue-Azure II-Basic Fuchsin (MBBF). Staining with MBBF is more controllable than with other methods and it requires only two short staining steps. Compared with Giemsa, MBBF provides a polychromatic, as opposed to a monochromatic end-result, sharply contrasting fibrin (blue) against collagen (pink-violet).

Interaction of macrophages and lymphocytes in rat skin allografts

Light microscopy of 2 microgram sections of rejecting rat skin allografts, embedded in hydroxyethyl methacrylate, revealed among the cells infiltrating the graft base extravascular macrophages containing a small lymphocyte. Toluidine blue staining indicated DNA degradation in some of these phagocytosed lymphocytes. More frequently small lymphocytes were in intimate contact with the surface of the macrophages, resembling "Periopolesis', which others have previously observed in vitro. These macrophage-lymphocyte interactions were not seen in sections of autografts. Despite a previous report that diphenylhydantoin (phenytoin) impairs macrophage function, these macrophage-lymphocyte interactions were present in grafts placed in rats receiving this drug. This treatment did not hasten or delay the onset of graft rejection. These in vivo findings both accord with recent in vitro studies on the mechanisms of phagocytosis and with reports that phagocytosis is one of the effector mechanisms in allograft rejection. However, macrophage phagocytosis of lymphocytes has also been observed in testicular lymph collected from conscious normal sheep.