IL-4 and IL-12 Regulate Proteoglycan-Induced Arthritis Through Stat-Dependent Mechanisms

Abstract

IL-4, a well-recognized modulator of macrophage activation, is perceived as an anti-inflammatory cytokine; however, under certain circumstances IL-4 may function as a proinflammatory cytokine. We have previously demonstrated that IL-4 treatment of mice with proteoglycan-induced arthritis (PGIA) inhibited the development of disease. To determine whether the capacity of IL-4 to inhibit disease is dependent on IL-4-mediated regulation of IL-12, we assessed the requirement for IL-4 in modulating development of PGIA. Immunization of mice, lacking IL-4 and Stat6, with proteoglycan results in a significant increase in arthritis severity in comparison to wild-type controls, suggesting that arthritis severity is regulated by IL-4 through a Stat6-dependent mechanism. Concomitant with exacerbated disease in IL-4−/− mice, there is a significant increase in the systemic production of proinflammatory cytokines IL-12, TNF-α, and IFN-γ and in levels of mRNA transcripts for proinflammatory cytokines and chemokines in joints. Disease is suppressed in Stat4−/− mice indicating that elevated levels of IL-12 contribute to exacerbation of arthritis and that suppression is accompanied by reduced levels of IFN-γ production. In support of this, IFN-γ−/− mice are protected from PGIA and the degree of inflammation is similar to Stat4−/− mice. The decrease in disease severity in IFN-γ−/− and Stat4−/− mice correlates with diminished TNF-α levels but there is no switch to a Th2-type response. Taken together, these results suggest that IL-4 regulates the severity of disease in PGIA by controlling IL-12 production, which in turn regulates the magnitude of IFN-γ expression through a Stat4-dependent pathway.

Interleukin‐4 regulates proteoglycan‐induced arthritis by specifically suppressing the innate immune response

“…Female mice ages 12-16 weeks were immunized intraperitoneally (IP) with 150 g human PG emulsified in Freund's complete adjuvant (CFA), as described (7,10). At weeks 3 and 6, mice received booster immunizations with 100 g PG in Freund's incomplete adjuvant.…”

“…We specifically tested the requirement for IFN␥ because development of PGIA is dependent on IFN␥ and STAT-4, and IL-4 has been shown to inhibit several components of the Th1 pathway, in particular STAT-4, IL-12R␤2, and T-box expressed in T cells (T-bet) (7,18). T cell IL-2 production was assessed in culture supernatants from T cells activated with human PG in the presence of irradiated naive splenocytes.…”

“…Thus, IL-4 may regulate the activation of resident synovial macrophages reducing infiltration of other leukocytes into the joint. In addition, elevated production of IFN␥ by T cells and a dramatic increase in the PG-specific antibody of the IgG2a isotype were observed in IL-4 Ϫ/Ϫ mice (7,8). Consequently, there are several ways in which IL-4 may regulate the onset and severity of PGIA.…”

“…In PGIA, we further showed that arthritis is exacerbated in IL-4 Ϫ/Ϫ mice, and IL-4 mediates this effect through activation of STAT-6 (7). Aggravated arthritis in IL-4 Ϫ/Ϫ mice is associated with an increase in chemokine (macrophage inflammatory protein 1␤ [MIP-1␤], MIP-1␣, MIP-2, and monocyte chemoattractant protein 1 ) and cytokine (IL-12p35, IL-1␤, IL-6, and TNF␣) transcripts in joints before development of any signs of inflammation or cellular infiltration (7). Thus, IL-4 may regulate the activation of resident synovial macrophages reducing infiltration of other leukocytes into the joint.…”

“…The ability of IL-4 to suppress Th1 cell differentiation and IFN␥ production has suggested that a switch from a Th1 response to a Th2 response might be responsible for the ability of IL-4 to control disease (7,10). IL-4 has been shown to inhibit STAT-4 induction, IL-12R␤2 expression, and the transcription factor T-bet (18).…”