Asteroid bodies: derivatives of the cytosphere. An electron microscopic contribution to the pathology of the cytocentre.

An electron microscopic study of asteroid bodies in granulomatous diseases of man, in particular in sarcoidosis and foreign body reactions, has led to the following conclusions. 1. Asteroid cytoplasmic inclusions are composed of organic proteineous structures. The body and arms of the stars consist mainly of longitudinally orientated, partially helically wound, collagen free, microfilaments with a diameter of approximately 50 A. Microtubules participate in their composition to a lesser degree. The filaments intertwine in various directions within the corpus of the stars. 2. Deeply osmiophilic compact structures, considered to represent condensation forms of protein, are consistently present within the body of the stars. These structures are partially granular and partially ring-shaped; in the latter case, transverse sections of tubules are noted. Since it is disputed whether they constitute procentrioles or postcentrioles, they are best referred to as paracentrioles. 3. The asteroid bodies are derivatives of the cytosphere, thus relating, in the broad sense, to the microfilamentous and microtubular apparatus of the cell. 4. The asteroid bodies in multinucleated giant cells participate in the spatial compartmentalization of the cytoplasmic content and nuclei. The sphere, aided by the centrioles, induces the formation of the mitotic spindle and, in addition, function as an organizing system of the cell. 5. The light microscopical periastral clear zone does not correspond to a fluid space. Rather, it consists of closely packed accumulations of laminated and whorled myelin figures, which are derived from the degradation of lipoid substances.