Cytological events in allo-stimulated lymphocytes triggered by exposure to stimulatory alloantigens. II. Changes in the areal density of cytoplasmic vacuoles and in the subcellular localization of acid phosphatase.

H-2b lymphocytes were sensitized against H-2d alloantigens by lymphocyte culture reaction and incubated with H-2d mastocytoma cells. The interaction between lymphoid cells and mastocytoma cells was stopped by fixation with glutaraldehyde. The areal density of the cytoplasmic vacuoles as well as the subcellular localization of acid phosphatase in lymphocytes were examined by electron microscopy. Two populations of lymphocytes were observed, small lymphocytes with heterochromatic nuclei and larger lymphocytes (lymphoblasts) with euchromatic nuclei. Only the lymphoblasts showed change following interaction with target cells. The vacuole area in percent of cytoplasmic area (vacuole areal density) of sensitized lymphoblasts increased during the first 30 minutes and from the third to fourth hour of interaction with target cells. Acid phosphatase staining was observed in the Golgi apparatus of the lymphoblasts after 30 minutes of interaction. Multivesicular bodies showed acid phosphatase staining within 20 minutes of interaction with target cells. After 20 minutes of interaction, phagosomes containing myelin figures were formed. These phagosomes also showed acid phosphatase staining and during the next hours of interaction their number increased over the number of multivesicular bodies.