Fine structure of the Kupffer cell in the bat, with special reference to the worm-like bodies

The livers from normal bats captured in summer and autumn (active period) and in winter (hibernating period) were electron microscopically examined with reference to the worm-like bodies. 1) The worm-like bodies were numerous in bats captured in the active periods, while they were few in hibernating bats. The development of this body varied considerably from cell to cell. 2) The worm-like body seemed to develop from a short and straight tubular invagination of the plasma membrane, whereas the fully developed unit of the body comprised a twisted and complicatedly branching tubule extended in the cytoplasm, the end of which seemed to be retained as the orifice to the extracellular space. The contents of the tubule continuous with the cell coat showed faint transverse striation and a median dense line. A large worm-like body was presumably composed of a number of the units tangled complicatedly with each other, showing a large accumulation of abundant profiles of closely packed tubules. In some Kupffer cells a long tortuous tubule with a median dense line penetrated the cytoplasm transversely and communicated at both ends with two opposite surfaces facing the sinusoid. 3)The cytoplasmic area of the worm-like bodies was almost completely devoid of organelles; no communication between the worm-like bodies and other organelles was recognized. This finding suggested the resemblance of the area of the worm-like bodies to the ectoplasm. This assumption also was supported by frequent occurence of large coated vesicles along the worm-like bodies often communicating with them. 4)The worm-like bodies did not show any signs of enlargement even in Kupffer cells ingesting blood cells in their phagocytic vacuoles. Their profiles were found abutting on the phagosomes, but direct communication between both structures was not found. 5)It was proposed in this study that the worm-like bodies might possibly represent a membrane reservoir and contribute to the enlargement of the Kupffer cell surface.