Proliferation rates of first- and fourth-passage FB
The proliferation rates of skin-FB and SFB were determined and the different preparations compared.

Isolated first-passage FB versus conventional fourth-passage FB
At rest, the proliferation rates of conventional fourth-passage normal skin-FB did not significantly differ from those of the corresponding cells in first passage (Fig. 8A). The same was true for conventional fourth passage OA-SFB and RA-SFB (Fig. 8B,C). Upon stimulation with PDGF (2.5 and 5 U/ml for all cells, 10 U/ml only for OA-SFB), however, the proliferation rates of skin, RA, and OA conventional fourth-passage FB were significantly higher (maximum mean increase, 5.4-fold) than those observed in first-passage cells (Fig. 8A,B,C). Following stimulation with IL-1β, in contrast, only conventional fourth-passage RA-SFB (150 U/ml IL-1β) showed significantly higher proliferation rates than first-passage cells (Fig. 8C).

Isolated first-passage versus isolated fourth-passage OA-SFB and RA-SFB
The proliferation rates of isolated fourth-passage cells in OA-SFB differed significantly from those of isolated first-passage cells only upon stimulation with IL-1β (50 and 150 U/ml; Fig. 8B). Such differences were not observed at rest or following stimulation with PDGF.
Isolated fourth-passage RA-SFB, in contrast, showed significantly higher proliferation rates than first-passage cells upon stimulation with all concentrations of IL-1β and PDGF, but not at rest (Fig. 8C).

Conventional fourth-passage versus isolated fourth-passage OA-SFB and RA-SFB
The proliferation rates of isolated fourth-passage SFB in both OA and RA were comparable with those of conventional fourth-passage SFB, whether at rest or PDGF-stimulated (Fig. 8B,C). Stimulation with IL-1β (at all concentrations), in contrast, induced significantly higher proliferation in isolated fourth-passage RA-SFB than in conventional fourth-passage RA-SFB (Fig. 8C). This difference was specific for RA-SFB, since it was not observed in OA-SFB (Fig. 8B).
As a consequence of differential IL-1β sensitivity in RA-SFB and OA-SFB, there were significant differences between isolated fourth-passage RA-SFB and OA-SFB (P ≤ 0.05; RA>OA, for 100 U/ml IL-1β), as well as between conventional fourth-passage RA-SFB and OA-SFB (P ≤ 0.05; OA>RA, for 50 and 150 U/ml IL-1β; Fig. 8B,C).