Article Text

  1. JN Stannard1,
  2. TJ Reed1,
  3. JM Kahlenberg1,
  4. EM Myers2,
  5. L Lowe3,
  6. JE Gudjonsson3
  1. 1Internal Medicine, Division of Rheumatology, University of Michigan, Ann Arbor, Michigan, United States
  2. 2Internal Medicine, Division of Rheumatology, Georgetown University, Washington, District of Columbia, United States
  3. 3Dermatology, University of Michigan, Ann Arbor, Michigan, United States


Background Cutaneous lupus erythematosus (CLE) is a disfiguring disease that can affect up to 70% of patients with systemic lupus. Treatment modalities are often ineffective and flares are frequent. Interleukin-6 (IL-6) is a pro-inflammatory cytokine which has gotten recent attention in SLE as IL-6 is increased in the serum of active patients and blockade of IL-6 is therapeutic in murine lupus models and phase I human trials. The source of IL-6 in CLE remains unclear.

Methods All studies were approved by the University of Michigan Internal Review Board (IRB# 72843 and 66116 to JMK). RNA was isolated from formalin fixed, paraffin-embedded biopsies of CLE rashes, which were obtained from the University of Michigan Pathology database. Real-time PCR was used to determine the expression level of the myxovirus (influenza virus) resistance 1 (MX-1) and interleukin-6 (IL6) genes. Biopsies were stained for IL-6 using immunohistochemistry. Skin biopsies were obtained from uninvolved skin of SLE patients with a history of cutaneous involvement or healthy controls followed by isolation and culture of keratinocytes. At confluence, cultures were treated with various concentrations of TLR ligands or UVB and IL-6 release was measured via ELISA. Blockade of type I IFN signaling was completed via monoclonal antibody to the type I IFN receptor.

Results Real-time PCR analysis of subacute cutaneous lupus erythematosus (sCLE) (n=21) and discoid (DLE) (n=22) rashes demonstrated a significant upregulation of both the IFN-regulated gene, MX1, and the pro-inflammatory cytokine IL-6 when compared with control samples (n=9). Immunohistochemical analysis of skin biopsies confirmed upregulation of IL-6 in the epidermis when compared to control. Keratinocytes from healthy skin of lupus patients produced significantly more IL-6 when stimulated by TLR2, 3 or 4 agonists or exposed to UVB radiation when compared to identical passage keratinocytes from healthy controls. Treatment of control keratinocytes with IFNα increased their IL-6 production and blockade of type I IFNs in the culture media of SKE keratinocytes downregulated the secretion of IL-6.

Conclusions IL-6 is increased at the RNA and protein level within cutaneous lupus biopsies when compared to healthy control skin. Keratinocytes are a major producer of IL-6 in the skin and lupus keratinocytes have enhanced production of IL-6 in response to TLR ligands and UV radiation. Exposure to type I IFN can increase IL-6 production in keratinocytes. SLE-derived keratinocytes downregulate IL-6 production in the presence of tonic blockade of the type I IFN receptor. These data suggest that the epidermis, which is an important barrier for environmental insults, is primed for IL-6 production by autocrine type I IFN production and that this may be one mechanism by which factors such as UV exposure may trigger rash development. Further investigations should focus on the pathogenic significance of IL-6 upregulation in the skin and whether targeting this pathway will have an impact on cutaneous disease activity.

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