Heat as a probe of centrosomal function: a phase-contrast and immunofluorescent study of human blood monocytes

In normal human blood monocytes, the nucleus is indented by the centrosome, which excludes the phase-dense granules that are spread throughout the cytoplasm. Within this paranuclear region, the paired centrioles are marked by immunofluorescent staining with an anti-centrosome antibody directed against the pericentriolar osmiophilic material that appears to serve as microtubule-organizing centers (MTOCs). Congruent paired structures are seen in phase-contrast. Following heat treatment (45 degrees C, 9 min), granules are retracted about a less indented nucleus, and anti-centrosome immunofluorescence is absent or very weak, even though paired centrosomal structures remain at least as phase-dense as in controls. Immunofluorescent staining with antimicrotubule antibody is also essentially lost following heat treatment. These findings are consistent with a heat-induced lesion in the pericentriolar osmiophilic material, which may prove generally useful as a probe of centrosomal function.