Cytokine Gene Activation in Synovial Membrane, Regional Lymph Nodes, and Spleen during the Course of Rat Adjuvant Arthritis

Cytokine gene activation was assessed during rat adjuvant arthritis (AA) in synovial membrane (SM), popliteal lymph node (popl-LN), and spleen, using semiquantitative, competitive RT-PCR. Changes in the popl-LN were considerably higher than in spleen or SM. In the preclinical phase (day 6), cytokine mRNA elevations occurred exclusively in the popl-LN and included IFN-γ, IL-1β, IL-5, IL-6, and IL-10. In the acute phase (days 13–16) all three organs became involved: (i) in the SM, significant elevations were limited to IL-1β and IL-6, which, notably, correlated positively with the degree of arthritis; (ii) in the popl-LN, IFN-γ, IL-1β, IL-6, and IL-10 (but not IL-5) were still elevated, while IL-2 rose significantly; (iii) in the spleen, TNF-α peaked simultaneously with the arthritis score (day 16) and dramatically dropped thereafter. Upon transition into the chronic phase (day 20) the following phenomena were observed: (i) IL-1β and IL-6 were still significantly increased in the SM; (ii) IFN-γ, IL-1β, IL-2, IL-6, and IL-10 were still elevated in the popl-LN; and (iii) there was a progressive rise of IL-5 mRNA in the spleen, positively correlated with the arthritis score. In conclusion, cytokines with pro- and anti-inflammatory functions overlap throughout disease, but in different organ-related patterns. Local (SM) and regional (popl-LN) IL-1β and IL-6, elevated throughout the entire course of AA, may directly contribute to disease severity. While in AA spleen TNF-α appears to be a systemic marker of acute disease, spleen IL-5 may be involved in disease resolution.