Background Interleukin-2 (IL-2) is a pro-inflammatory cytokine and exacerbates Th-1 mediated diseases such as autoimmune arthritis. However, IL-2 also induces regulatory T cells (Tregs) and reduces disease activity such as systemic lupus erythematosus. IL-2/anti-IL-2 monoclonal antibody immune complex (IL-2IC) increases the half life of IL-2 in vivo and strongly induces Tregs. Administration of IL-2IC has been reported to suppress experimental autoimmune diseases and graft-versus-host diseases.
Objectives To clarify complex regulatory network of IL-2 and cellular interactions involved in autoimmune arthritis we examined the effects of IL-2IC administration during the course of collagen-induces arthritis (CIA) model.
Methods Male DBA/1 mice were immunized by injection of 200μg of Type II collagen emulsified with an equal volume of Complete Freud Adjuvant intradermally at the base of the tail of mice (first immunization). Second immunization was given 21 days after first immunization. IL-2ICs were prepared by mixing 5μg of anti-IL-2 antibody (clone JES6-1D) with 1μg of mouse IL-2 for 15 minutes. The mice were injected with either PBS as a control or IL-2IC (5μg /mouse) intraperitoneally for 3 days. Mouse paws were scored for arthritis using a macroscopic scoring system ranging from 0 to 4 (0, no swelling or redness; 1, swelling/redness of paw or one joint; 2, two joints involved; 3, more than two joints involved; and 4, severe arthritis of the entire paw and joints). The arthritic score for each mouse is the sum of the scores of all four paws. Peripheral blood cells were stained with anti-CD25 (PC61), anti–CD4 (RM4-5), anti-Foxp3 (FJK-16s) and CD4+CD25+Foxp3+ Tregs were analyzed by flow cytometry. Statistical analysis was performed by paired t test.
Results To define the effect of IL-2IC on established CIA, IL-2IC was administered for 3 days from day 21 to day 23 after the first immunization (day 0 to day 2 after the second immunization) of CIA. Treatment with IL-2IC significantly enhanced the onset of arthritis and increased the severity of disease, demonstrating that IL-2IC is pro-inflammatory and exacerbates the disease activity when administered during established CIA. To define the effect of IL-2IC on early stages of disease induction we next administered IL-2IC from day 14 to day 16 after first immunization (from day -7 to day -5 of the second immunization) and observed a significant decrease in both the incidence and severity of arthritis. Injection of IL-2IC effectively elicited expansion of CD4+CD25+Foxp3+ Tregs in peripheral blood cells (IL-2IC vs PBS control:21.2% vs 10.3% in CD4+ T cells on day 4 after IL-2IC administration). The increase of CD4+CD25+Foxp3+ Tregs was observed in both established and early stage of clinical disease of CIA.
Conclusions These observations indicate that IL-2IC might play a complex regulatory role in autoimmune arthritis depending on the timing of administration. Although IL-2IC is pro-inflammatory in established disease and increases the severity of the disease, it can play an anti-inflammatory role during early stages of disease by the induction of Tregs.
Disclosure of Interest None declared