Allograft cytotoxicity: differences between lytic and non-lytic interactions as revealed by ultrastructural histochemistry.

Alloimmune and normal mouse (C57Bl/10) spleen cells and tumour cells (P815Y) were cultured together in flat-bottomed microtitre plates. Cytolytic activity was assessed by the 51Cr release assay in combination with histological analyses. Cells were fixed and embedded in situ and substrates to reveal ATPase or, alternatively, endogenous peroxidase activities, were applied. Both lymphocytes and monocytes formed junctions with the target cells and estimates of their relative frequencies were produced. Junctions between lymphocytes and tumour cells were completely ablated by treatment with anti-brain-associated theta and complement. Junctions involving immune lymphocytes were typically associated with locally increased ATPase activity in the target cell membrane. Neither monocytes nor normal lymphocytes increased local ATPase activity or 51Cr release to any significant extent.