Journal Article

The nature of the post-translational modifications of the autoantigen LL37 influences the autoreactive T-helper cell phenotype in psoriasis

Facheris, Paola, Mancini, Flavia, Botti, Elisabetta, Mennella, Anna, Palazzo, Raffaella, Frasca, Loredana, Ocone, Giuseppe, Pietraforte, Immacolata, Costanzo, Antonio, Favaro, Rebecca, Lande, Roberto, Falchi, Mario, Conrad, Curdin, Bianchi, Luca

2025

Overview

Psoriasis is a chronic skin disease evolving to psoriatic arthritis (PsA) in 30% of cases. LL37 is a psoriasis T-cell autoantigen and, in complex with self-DNA/RNA, a trigger of type I interferon (IFN-I) and pro-inflammatory factors in dendritic cells. LL37 can undergo irreversible post-translational modifications (PTMs), namely, citrullination and carbamylation, which are linked to a neutrophil-dominated inflammation. Notably, in PsA, carbamylated and citrullinated LL37 (carb-LL37 and cit-LL37) become antibody targets. Here, we analyze the presence of, and the T-cell and antibody reactivity to, cit-LL37 and carb-LL37, to address the occurrence and significance of these PTMs in psoriasis. The presence of modified LL37 in skin biopsies was assessed by laser scanner confocal microscopy (LSCM); T-cell responses to modified LL37 were assessed by Ki67 assay and intracellular cytokine staining using flow cytometry; serum autoantibodies to the same antigens were tested by enzyme-linked immunosorbent assay (ELISA). The results show that native and modified LL37 (both carb-LL37 and cit-LL37) are detectable in psoriatic skin, but not in healthy donors’ (HD) skin, where they colocalize with neutrophil infiltrates and neutrophil extracellular trap formation (NETosis). Psoriatic T cells and antibodies recognize native LL37, cit-LL37, and carb-LL37, but only CD4-T-cell responses to native LL37 and carb-LL37 correlate with psoriasis area severity index (PASI), whereas CD8-T-cell responses to the same peptides correlate with PASI in the HLA-Cw6*02-positive subgroup. CD4-T cells specific for modified LL37 express heterogeneous T-helper (Th) phenotypes: native/carb-LL37-specific T cells mainly manifest a Th1/Th17-like phenotype, whereas cit-LL37-specific T cells resemble Th-follicular (Thf)-like cells. In vitro T-cell polarization experiments suggest that distinct pro-inflammatory effects of LL37 and modified LL37, in complex with self-nucleic acids, may concur to these phenomena. This is the first evidence in psoriasis that PTMs of an autoantigen with innate immune cell stimulatory ability dictate autoreactive Th-cell polarization. These data, obtained using LL37 as a model autoantigen, indicate that citrullination and carbamylation pathways may play a role in the psoriasis course, generating epitopes to which immunological tolerance does not exist and potentially concur to PsA development.

• Publisher: Frontiers Media SA,Frontiers Media S.A
• Subject: Adaptive immunity / Adult / Aged / Antigens / Arthritis / Autoantibodies / Autoantibodies - blood / Autoantibodies - immunology / autoantigens / Autoantigens - immunology / Autoantigens - metabolism / Autoimmunity / autoreactive responses / Biopsy / Carbamylation / Cathelicidins - immunology / Cathelicidins - metabolism / CD4 antigen / CD8 antigen / Chronic illnesses / Citrullination / Citrulline / Confocal microscopy / Cytokines / Dendritic cells / Enzyme-linked immunosorbent assay / Epitopes / Female / Flow cytometry / Genotype & phenotype / Helper cells / Humans / Immunological tolerance / Immunology / Inflammation / Interferon / Leukocytes (neutrophilic) / LL37 / Lymphocytes / Lymphocytes T / Male / Middle Aged / Monoclonal antibodies / Neutrophils / Pathogenesis / Phenotype / Phenotypes / Polarization / Post-translation / Protein Processing, Post-Translational - immunology / Psoriasis / Psoriasis - immunology / Psoriasis - metabolism / Psoriasis - pathology / Psoriatic arthritis / Skin - immunology / Skin - pathology / Skin diseases / T-Lymphocytes, Helper-Inducer - immunology / T-Lymphocytes, Helper-Inducer - metabolism / Translation / Tumor necrosis factor-TNF