IL13 and rheumatoid arthritis: By drawing comparisons with RA FLS subjected to hypoxia alone, we found that HIF-1α transcript was induced by Th1 cytokines TNFα and IL-1β (on average 7.4-fold and 3.5-fold, respectively), but not by Th2 cytokines IL-4 (Figure 3a) and IL-13 (data not shown).