Alloantigen-specific proliferation is dependent on interactions between CCR1 and CCL5. Allospecific proliferation was assessed in vitro during a mixed lymphocyte reaction in either flat-bottom or round-bottom plates using CCR1^+/+ (■) or CCR1^−/− (▩) T cells with B6D2F1 stimulators or control media as described in Figure 5. Data are presented as means plus or minus SEM and are from 1 of 3 similar experiments; *P < .001.