Characterization of cells involved in the formation of granuloma. An ultrastructural study on macrophages, epitheloid cells, and giant cells in experimental tubulo-interstitial nephritis.

In experimental tubulo-interstitial (anti-basement membrane) nephritis of the rat, granulomatous inflammation develops around immunologically altered tubular basement membranes. The present light- and electron microscopic studies indicate that in the course of the granulomatous reaction, tissue monocytes evolve from blood monocytes and pursue two independent pathways of differentation. On the one hand they may differentiate into macrophages ("distant from tubules") or, alternatively, into epitheloid cells ("adjacent to tubules"). The latter, through cell fusion, develop into multinucleated giant cells of the Langhans' type. The cytoplasmic components of the epitheloid cells and the multinucleated giant cells should be interpreted as an activation of cellular biosynthesis. Its products, upon being secreted at the immunodefective basement membrane, will obviously serve immune defense mechanisms.