Abolition of CTL activity in pfp^−/− mice. CTL activity was determined by ⁵¹Cr release assay. (A) Equal numbers of splenic T cells from a 6-day primary MLR (B6 anti-B6D2F1) were used as effectors. (B) Splenocytes from day 7 posttransplant (n = 5/group) were counted, and equal numbers of T cells (CD4⁺ plus CD8⁺ cells adjusted according to FACS analysis) were used as effectors.⁵¹Cr-labeled p815 targets (H-2^d) were coincubated with effectors for 4 hours, and ⁵¹Cr in the supernatants was determined by a γ-scintillation counter.