Effect of interleukin (IL)-17 and prostaglandin E1 (PGE1) on pannus-like tissue growth in vitro. Synovial tissue (ST)-derived inflammatory cells were incubated in the absence or presence of increasing concentrations of IL-17 (0 to 100 ng/ml) (n = 17) or PGE1 (100 nM) (n = 9). Morphologic changes were observed under an inverted phase contrast microscope twice weekly for 4 weeks and were scored semiquantitatively on a scale of 0 to 4 according to the degree of tissue development as described in Materials and methods. Box and whisker plots indicate 25th/75th percentile and minimum/maximum, respectively. Bar indicates the median value. *P < 0.001 (by Mann-Whitney U test).