Cytokine expression was assessed during antigen-induced arthritis in the synovial membrane, inguinal lymph node, and spleen using competitive RT-PCR and sandwich ELISA

In the synovial membrane, early mRNA elevations of IL-1β and IL-6 (6 hours; 450-fold and 200-fold, respectively) positively correlated with the joint swelling. A sixfold tumour necrosis factor alpha increase was not significant. Not only IL-2 and interferon gamma (IFN-γ) (10⁴-fold and 200-fold, respectively), but also IL-5 and IL-10 increased acutely (6 hours–day 1; threefold and 35-fold, respectively). In general, the protein levels for IL-1β, IL-6, tumour necrosis factor alpha, IFN-γ, IL-4, and IL-10 (increase between fourfold and 15-fold) matched the course of mRNA expression.

In the inguinal lymph node there were early mRNA elevations of IL-6 (6 hours; 2.5-fold; positively correlated with the joint swelling) and IL-2 (6 hours; fourfold), as well as later rises of IL-4 and IL-5 (day 3; 2.5-fold and fourfold, respectively). At the protein level no significant elevations were observed in comparison with day 0, except for IL-1β (day 6) and IL-10 (day 1).

In the spleen, there were significant mRNA elevations at 6 hours of IL-1β (1.5-fold), IL-6 (fourfold; positively correlated with the joint swelling), IFN-γ (threefold), and IL-2 (sevenfold to 10-fold). IL-5 and IL-10 (twofold and threefold, respectively) peaked from 6 hours to day 3. Increases at the protein level were significant compared with day 0 only in the case of IL-2 (day 6).

By day 6 (transition to the chronic phase) the mRNA for cytokines declined to or below pre-arthritis levels in all organs, except for IL-1β in the synovial membrane and IL-6 in the spleen. antigen-induced arthritis is thus characterized by: early synovial activation of macrophages, Th1-like, and Th2-like cells; late, well-segregated Th2-like responses in the inguinal lymph node; late, overlapping Th1-like/Th2-like peaks in the spleen; and chronic elevation of synovial IL-1β mRNA and spleen IL-6 mRNA.