Scanning electron microscope (SEM) observations were conducted mainly on the in vitro interaction state between ]TC-II cells derived from Ehrlich ascites tumor and regional lymph node cells obtained from the mice I0 days after transplantation of Ehrlich ascites tumor. Cells cultured on the cover glass were fixed with glutaraldehyde, dehydrated with
graded acetone solution, and covered with carbon and gold, were observed by SEM. The results may be briefly summarized as follows. On the surface of ]TC.II cells themselves are seen numerous fine microvilli projecting out regularly at right angle to the cell surface, which become attached to the glass, and there can be observed vacuoles in the cytoplasm. Such microvilli are lacking at the tip of the pseudopodial projection. The lymph node cells aggregated to ]TC-II cell are lymphocytes of small or intermediate size, and the pattern of aggregation varies: some lymphocytes effect an intimate contact with the surface of target cell by their cellular projections; the contact is achieved by interdigitation of microvilli between lymphocyte and target cell; b:>th cells form a bridge connection with a simple projection from each; or the two cells make a broad surface.to.surface contact.
It is not possible to differentiate sensitized lymphocyte from nonsensitized one, their cell shape is spherical with rough surface and some cells show hole on the surface.</p
