Differentiation of granuloma cells (epithelioid cells and multinucleated giant cells): a morphometric analysis. Investigations using the model of experimental autoimmune (anti-TBM) tubulo-interstitial nephritis.

Morphometric analysis disclosed distinct differences between blood monocytes, tissue monocytes (i.e. immature macrophages), epithelioid cells and multinucleated giant cells as well as phagocytic macrophages (i.e. mature macrophages) in the granuloma model of autoimmune (anti-TBM) tubulo-interstitial nephritis. The numerical density of lysosomes decreased slightly in tissue monocytes compared with blood monocytes but showed a pronounced increase during the formation of epithelioid cells. The lysosomal compartments of epithelioid cells and multinucleated giant cells resembled each other very closely, but the giant cells obviously produced additional lysosomes of small diameter (80-120 nm). Phagocytic macrophages displayed a total numerical density of lysosomes similar to that of tissue monocytes but the mean diameter of the lysosomes was markedly greater. Thus the volume density of lysosomes was highest in phagocytic macrophages. The blood monocytes exhibited the smallest lysosomal compartment. In tissue monocytes, epithelioid cells, and multinucleated giant cells the volume densities of the lysosomes were greater than in blood monocytes and remained relatively constant because the increase in numerical density was counterbalanced by a decrease in mean granule diameter. We found only minor differences in mitochondrial volume densities among the five cell populations. The shape of the mitochondria, however, changed steadily from short rotational ellipsoids in the blood monocytes to rather elongated and slender bodies in the multinucleated giant cells. The results suggest that epithelioid cells and multinucleated giant cells are active cells which may contribute by their specific performances, to the immunologic microenvironment of the granuloma.