MORPHOLOGICAL ASPECTS OF GIANT-CELLS IN GIANT-CELL ARTERITIS - AN ELECTRON-MICROSCOPIC AND IMMUNOCYTOCHEMICAL STUDY

Objectives, To compare the morphology of foreign body and Langhans gia nt cells in the two different inflammatory phases of giant cell arteri tis (GCA). Methods. Electron microscopy was performed on 6 positive te mporal arterial biopsies. Light microscopy and immunocytochemistry for macrophage-associated antigen (KP1) and alpha-smooth muscle actin (al pha-SMA) were performed on 16 positive biopsies. Results. A focal gran ulomatous reaction with foreign body giant cells was found only in ass ociation with the internal elastic membrane (IEM) in atrophic arterial segments, which often displayed calcification of the IEM. Diffuse inv asion of lymphocytes and monocytes/macrophages affected non-atrophic a s well as atrophic arterial segments. Within such segments Langhans gi ant cells were found in all layers of the wall. Electron microscopy of biopsies displaying the focal foreign body reaction revealed that lar ge cells devoid of lysosomes but with cytoplasmic densities, tightly p acked cytoplasmic filaments and numerous micropinocytotic vesicles for med clusters close to calcified parts of the internal elastic membrane . Furthermore, foreign body giant cells were surrounded by large cells devoid of lysosomes. Lysosomes tended to concentrate in central parts of the foreign body giant cells. In the diffusely inflamed arteries, the Langhans giant cells were surrounded by mononuclear cells rich in lysosomes. The lysosomes in the Langhans giant cells were more evenly distributed than in foreign body giant cells. Immunocytochemistry of b iopsies displaying the focal granulomatous reaction revealed an uneven , often central immunoreactivity for the macrophage marker (KP1) in th e foreign body giant cells, and immunostaining for alpha-smooth muscle antigen (alpha-SMA) showed their poor delineation from the surroundin g vascular smooth muscle cells. The Langhans giant cells in the diffus ely inflamed arteries displayed a strong even cytoplasmic immunoreacti vity for KP1 and a distinct delineation from the smooth muscle cells i n the alpha-SMA staining. Conclusion. Differences in terms of distribu tion, light microscopy, immunocytochemistry and electron microscopy be tween the two types of giant cells in GCA indicate a difference in the ir function as well as their histogenesis.