Temporal requirement for antigen in primary and secondary MLC reactions

The requirement for antigen in primary and secondary mixed leukocyte culture was tested by removal of stimulating cells at various time points with antiserum plus complement. In the primary mixed leukocyte cultures, antigen was absolutely required for 24 hr and the need for antigen diminished essentially completely by 72 hr. In the primary mixed leukocyte culture, the antigen was required only for 6 to 9 hr. These findings are compared with other known parameters of in vitro generation of cytotoxic effector cells.