Platelets do not stimulate allospecific cytotoxicity even in the presence of nonspecific helper activity.

Responder PBMCs n°1 were stimulated twice with PBMCs n°2 or platelets n°2 in the presence or absence of PBMCs n°3 (see Materials and methods). Allostimulation against PBMCs n°3 alone was also performed as control. Resulting cytotoxic activity was tested at day 14 against autologous PBMC-PHA n°1 (open circles), allogenic PBMC-PHA n°2 (closed circles), or n°3 (closed triangles), at the indicated E:T ratios. Stimulating conditions are indicated at the top of each graph.