Effects of opposing cell types on growth, according to smoking status (panel A - left) and p27 SNP genotype (panel B - right). Current smoking decreases the inhibitory influence of adventitial cells on SMC growth, but not the stimulatory effect of SMCs on adventitial cells. N= 19 pairs of cells total, 13 for current smoking. *P<.01 smoking vs. no smoking. The protective AA p27 SNP genotype leads to more stimulation of adventitial cell growth by SMCs and a trend for more inhibition of SMC growth by adventitial cells. N=19 pairs of cells total, 10 for for AA. *P<.04, AA vs. CC.