IL-6 promotes acute and chronic inflammatory disease in the absence of SOCS3

Abstract

The lack of expression of the suppressor of cytokine signalling-3 (SOCS3) or inactivation of the negative regulatory capacity of SOCS3 has been well documented in rheumatoid arthritis, viral hepatitis and cancer. The specific qualitative and quantitative consequences of SOCS3 deficiency on interleukin-6 (IL-6)-mediated pro- and anti-inflammatory responses remain controversial in vitro and unknown in vivo. Mice with a conditional deletion of SOCS3 in hematopoietic cells develop lethal inflammatory disease during adult life and develop gross histopathological changes during experimental arthritis, typified by elevated IL-6 levels. To clarify the nature of the IL-6 responses in vivo, we generated mice deficient in SOCS3 (SOCS3(-/Δvav)) or both SOCS3 and IL-6 (IL-6(-/-)/SOCS3(-/Δvav)), and examined responses in models of acute and chronic inflammation. Acute responses to IL-1β were lethal to SOCS3(-/Δvav) mice but not IL-6(-/-)/SOCS3(-/Δvav) mice, indicating that IL-6 was required for the lethal inflammation induced by IL-1β. Administration of IL-1β to SOCS3(-/Δvav) mice induced systemic apoptosis of lymphocytes in the thymus, spleen and lymph nodes that was dependent on the presence of IL-6. IL-6 deficiency prolonged survival of SOCS3(-/Δvav) mice and ameliorated spontaneous inflammatory disease developing during adult life. Infection of SOCS3(-/Δvav) mice with LCMV induced a lethal inflammatory response that was dependent on IL-6, despite SOCS3(-/Δvav) mice controlling viral replication. We conclude that SOCS3 is required for survival during inflammatory responses and is a critical regulator of IL-6 in vivo.

Figure 1

(A) Survival of SOCS3^{−/Δ vav} mice is prolonged in the absence of IL-6. p<0.05, SOCS3^{−/Δ vav} v IL-6^−/−/SOCS3^{−/Δ vav}, by log-rank test. (B) Survival of mice reconstituted with SOCS3^{−/Δ vav} bone marrow is not different to mice reconstituted with wild-type bone marrow. Wild-type mice were reconstituted with SOCS3^{−/Δ vav} or wild-type bone marrow. p>0.05, SOCS3^{−/Δ vav} v wild-type, by log-rank test.

Figure 2

SOCS3 regulates responses to IL-1β in vivo. (A) SOCS3^{−/Δ vav} mice are hypersensitive to IL-1β, resulting from loss of regulation of IL-6. n=4–5 per group. (B) SOCS3 regulates cytokine production independently of IL-6 after challenge with IL-1β. Cytokine production was analysed in the serum of mice injected with IL-1β.

Figure 3

IL-1β induces loss of cells in the bone marrow (A) and apoptosis of leukocytes in the thymus (B) of SOCS3^{−/Δ vav} mice but not IL-6^−/−/SOCS3^{−/Δ vav} mice. Tissues were stained with haematoxylin and eosin. (C) Flow cytometric analysis of haemopoietic cells in the bone marrow from IL-1β-injected wild-type and SOCS3^{−/Δ vav} mice, 36 h after injection.

Figure 4

SOCS3 is essential for survival to LCMV but not essential for the generation of LCMV-specific CD8⁺ T cell responses or the containment of viral replication. (A) Mice that were moribund at day 7 of LCMV infection. (B) Hematopoietic cell populations were measured by flow cytometry on day 7 of LCMV infection. LCMV-specific CD8+ T cells were identified using tetramers specific for LCMV epitopes GP33-41, GP276-286 and NP396-404. (C) Viral titres in lung, kidney, liver and spleen were assessed on day 7. *p<0.05, ANOVA and SNK.