Complementary Effects of Carbamylated and Citrullinated LL37 in Autoimmunity and Inflammation in Systemic Lupus Erythematosus

Int J Mol Sci. 2021 Feb 6;22(4):1650. doi: 10.3390/ijms22041650.

Abstract

LL37 acts as T-cell/B-cell autoantigen in Systemic lupus erythematosus (SLE) and psoriatic disease. Moreover, when bound to "self" nucleic acids, LL37 acts as "danger signal," leading to type I interferon (IFN-I)/pro-inflammatory factors production. T-cell epitopes derived from citrullinated-LL37 act as better antigens than unmodified LL37 epitopes in SLE, at least in selected HLA-backgrounds, included the SLE-associated HLA-DRB1*1501/HLA-DRB5*0101 backgrounds. Remarkably, while "fully-citrullinated" LL37 acts as better T-cell-stimulator, it loses DNA-binding ability and the associated "adjuvant-like" properties. Since LL37 undergoes a further irreversible post-translational modification, carbamylation and antibodies to carbamylated self-proteins other than LL37 are present in SLE, here we addressed the involvement of carbamylated-LL37 in autoimmunity and inflammation in SLE. We detected carbamylated-LL37 in SLE-affected tissues. Most importantly, carbamylated-LL37-specific antibodies and CD4 T-cells circulate in SLE and both correlate with disease activity. In contrast to "fully citrullinated-LL37," "fully carbamylated-LL37" maintains both innate and adaptive immune-cells' stimulatory abilities: in complex with DNA, carbamylated-LL37 stimulates plasmacytoid dendritic cell IFN-α production and B-cell maturation into plasma cells. Thus, we report a further example of how different post-translational modifications of a self-antigen exert complementary effects that sustain autoimmunity and inflammation, respectively. These data also show that T/B-cell responses to carbamylated-LL37 represent novel SLE disease biomarkers.

Keywords: LL37; post-translational modifications (PTM); systemic lupus erythematosus (SLE).

MeSH terms

  • Adjuvants, Immunologic / metabolism*
  • Antimicrobial Cationic Peptides / metabolism*
  • Autoantibodies / immunology
  • Autoantigens / chemistry*
  • Autoantigens / immunology
  • Autoimmunity / immunology
  • B-Lymphocytes / immunology
  • CD4-Positive T-Lymphocytes / immunology
  • Cathelicidins
  • Citrullination / immunology
  • Dendritic Cells / immunology
  • Epitopes, T-Lymphocyte / immunology
  • HLA-DRB1 Chains / immunology
  • HLA-DRB5 Chains / immunology
  • Humans
  • Interferon Type I / immunology
  • Lupus Erythematosus, Systemic / immunology*
  • Lymphocyte Activation / immunology
  • Protein Carbamylation / immunology
  • Protein Processing, Post-Translational / genetics*

Substances

  • Adjuvants, Immunologic
  • Antimicrobial Cationic Peptides
  • Autoantibodies
  • Autoantigens
  • Epitopes, T-Lymphocyte
  • HLA-DRB1 Chains
  • HLA-DRB1*15:01 antigen
  • HLA-DRB5 Chains
  • Interferon Type I
  • Cathelicidins