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A method is presented by which cells growing as monolayers cultured in microtitre plates can be embedded for electron microscopy. The technique has the following advantages: numerous specimens may be prepared with relatively small numbers of cells, cell-cell interactions remain undisturbed and may be enumerated, and morphology can be studied under circumstances identical with those used in cell-mediated cytotoxicity assays.

We have examined, by transmission electron microscopy, mixtures of DNP-coated chicken red blood cells and normal human peripheral blood leucocytes 'armed' with alkali-aggregated anti-dinitrophenyl (DNP) antibody. The combination of these observations with chromium release assays enabled us to identify four types of effector cell interacting with the target erythrocytes, viz. phagocytic and non-phagocytic monocytes, neutrophils and lymphocytes. Comparison of these findings with previous work, using antibody-coated targets, allowed us to conclude that the mechanisms and cell types involved are similar. We also demonstrated the short-lived cytotoxic potential of cells armed in this manner.

Senile macular degeneration (SMD) is a leading cause of legal blindness in western countries. The role of immunocompetent cells in the pathogenesis of this disease has not been widely recognised. In this work specimens were studied by electron microscopy to provide ultrastructural details of the role of immunocompetent cells in early, intermediate and late stages of the disease. Additionally, we have analysed the frequency and distribution of inflammatory cellular infiltrates using wax histology. The results illustrate the involvement of macrophage-series cells, fibroblasts, lymphocytes and mast cells in neovascularisation, atrophy of the retinal pigment epithelium and the breakdown of Bruch's membrane. These observations, together with previous clinicopathological studies, have led us to suggest that SMD has a chronic inflammatory component.

Examination in the electron microscope of mouse spleen cells treated with conjugates of wheatgerm agglutinin and horseradish peroxidase has shown the surface of myeloid cells to be heavily stained. Resting lymphocytes were unstained but became positive after stimulation by phytohaemagglutinin or concanavalin A, suggesting a relationship between the presence of this surface component and the functional state of the cell and providing a further point of similarity between myeloid and lymphoblastoid cells. The conjugates have also been useful in tracing the fate of surface carbohydrates during phagocytosis.

We describe the ultrastructural features of subretinal neovascularisation associated with the pathogenesis of age-related macular degeneration (AMD). The choroidal origin of new vessels was confirmed, and ultrastructural details are presented. Serial sectioning of new vessels revealed a relationship between leucocytes and neovascular structures. The results are discussed in the context of the previously established role of leucocytes in angiogenesis. Our results provide circumstantial evidence, based on morphological observations, for the involvement of leucocytes in the promotion of neovascular proliferation and exudation from new vessels.

On the basis of electron microscopic observations, four types of cells apparently cytotoxic for antibody-coated chicken erythrocytes were identified in non-immune mouse spleen; monocytes, polymorphonuclear leucocytes, immature granulocytes and a type of lymphoid cell. Both phagocytosis and extracellular lysis of target cells were observed. Monocytes and polymorphonuclears were able to interact with the target cell by both mechanisms while the intermediary granulocytes and lymphoid cells were only capable of extracellular lysis. It is argued that these observations provide a morphological basis for the previous classification of antibody-dependent cytotoxic cells into myeloid and lymphoid cells (Greenberg et al., 1973b, 1975).