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The Surface Ultrastructure of Normal and Leukemic Rat Lymphocytes^*

( Department of Pathology, University of Pennsylvania School of Medicine, Philadelphia 4, Pa.)

The surface ultrastructure of normal and leukemic rat lymphocytes has been compared by electron microscopy. Large and small lymphocytes, both normal and neoplastic, from blood and lymph nodes, all showed a similar fine surface structure consisting of unevenly distributed particles 100–300 A in diameter.

Large cells, presumably reticulum cells, with 1000 A craters on their surface, were observed in all preparations except those from the circulating blood of the normal rat. Shaking experiments indicated that the intercellular adhesiveness of these "crater cells" was greater than that of the other cells in the nodes.

In the cell system used, the adhesiveness was low in both the normal and neoplastic cells. The failure to observe a difference in surface ultrastructure suggests that a change to the neoplastic state is not necessarily accompanied by an alteration in the cell surface—at least in rat lymphocytes.

Of all the cells examined, only reticulum cells showed a surface difference; and these cells also showed a greater adhesiveness. This suggests that the ultrastructure of the cell surface may be directly related to intercellular adhesiveness.

^* This investigation was supported by Senior Research Fellowship SF-4 from the Public Health Service and by Grant C-3562 from the National Cancer Institute of the National Institutes of Health, U.S. Public Health Service.

Received 5/19/58.