Surface features of small thymocytes of rat: a freeze-fracture and scanning electron microscope study.

The surface of small thymocytes of 6 day old rats has been examined by freeze-fracture and scanning electron microscopy. Various procedures were used to enrich the cell population and protect their surfaces. On the basis of morphological criteria, three types of small thymocytes: smooth thymocytes (79.5% of total cells), thymocytes characterized by the presence of ridge-like profiles (16.1%) and thymocytes displaying a moderate number of small microvilli (2.4%). From the results after stimulation with PHA and later separation, it is concluded that the first population corresponds to small cortical thymocytes, and the second to small medullary thymocytes.