Newt eosinophils are motile granulated leukocytes that uniquely display a highly visible centrosomal area. Electron microscope and tubulin antibody fluorescence confirms the presence of centrioles, pericentriolar material, and radiating microtubules within this visible area. Actin antibodies intensely stain the advancing cell edges and tail but only weakly stain pseudopods being withdrawn into the cell. Randomly activated eosinophils follow a roughly consistent direction with an average rate of 22.5 micron/min. The position of the centrosome is always located between the trailing cell nucleus and advancing cell edge. If the cell extends more than one pseudopod, the one closest to or containing the centrosome is always the one in which motility continues. Laser irradiation of the visible centrosomal area resulted in rapid cell rounding. After several minutes following irradiation, most cells flattened and movement continued. However, postirradiation motility was uncoordinated and directionless , and the rate decreased to an average of 14.5 micron/min. Electron microscopy and tubulin immunofluorescence indicated that an initial disorganization of microtubules resulted from the laser microirradiations . After several minutes, organized microtubules reappeared, but the centrioles appeared increasingly damaged. The irregularities in motility due to irradiation are probably related to the damaged centrioles. The results presented in this paper suggest that the centrosome is an important structure in controlling the rate and direction of newt eosinophil motility.

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