Granulysin-producing cytotoxic T cells in the mucocutaneous lesions of Behçet disease: a distinct inflammatory response from erythema nodosum

Reduction of Neutrophil Activation by Phosphodiesterase 4 Blockade in Behçet's Disease

OBJECTIVE

Behçet's disease (BD) is a systemic vasculitis with inflammatory lesions mediated by cytotoxic T cells and neutrophils. Apremilast, an orally available small-molecule drug that selectively inhibits phosphodiesterase 4 (PDE4), has been recently approved for the treatment of BD. We aimed to investigate the effect of PDE4 inhibition on neutrophil activation in BD.

METHODS

We studied surface markers and reactive oxygen species (ROS) production by flow cytometry, and neutrophil extracellular traps (NETs) production and molecular signature of neutrophils by transcriptome analysis before and after PDE4 inhibition.

RESULTS

Activation surface markers (CD64, CD66b, CD11b, and CD11c), ROS production, and NETosis were up-regulated in BD patient neutrophils compared to healthy donor neutrophils. Transcriptome analysis revealed 1,021 significantly dysregulated neutrophil genes between BD patients and healthy donors. Among dysregulated genes, we found a substantial enrichment for pathways linked to innate immunity, intracellular signaling, and chemotaxis in BD. Skin lesions of BD patients showed increased infiltration of neutrophils that colocalized with PDE4. Inhibition of PDE4 by apremilast strongly inhibited neutrophil surface activation markers as well as ROS production, NETosis, and genes and pathways related to innate immunity, intracellular signaling, and chemotaxis.

CONCLUSION

We highlight key biologic effects of apremilast on neutrophils in BD.

Immunopathogenesis of Behçet's disease

Behçet's disease (BD) is a multi-system inflammatory disorder with vasculitic features. It does not suit any of the current pathogenesis-driven disease classifications well, a unifying concept of its pathogenesis is not unanimously conceivable at present, and its etiology is obscure. Still, evidence from immunogenetic and other studies supports the notion of a complex-polygenic disease with robust innate effector responses, reconstitution of regulatory T cells upon successful treatment, and first clues to the role of an, as of yet, underexplored adaptive immune system and its antigen recognition receptors. Without an attempt to be comprehensive, this review aims to collect and organize impactful parts of this evidence in a way that allows the reader to appreciate the work done and define the efforts needed now. The focus is on literature and notions that drove the field into new directions, whether recent or more remote.

Behçet's disease risk-variant HLA-B51/ERAP1-Hap10 alters human CD8 T cell immunity

OBJECTIVES

The endoplasmic reticulum aminopeptidase (ERAP1) haplotype Hap10 encodes for a variant allotype of the endoplasmic reticulum (ER)-resident peptide-trimming aminopeptidase ERAP1 with low enzymatic activity. This haplotype recessively confers the highest risk for Behçet's diseases (BD) currently known, but only in carriers of HLA-B*51, the classical risk factor for the disease. The mechanistic implications and biological consequences of this epistatic relationship are unknown. Here, we aimed to determine its biological relevance and functional impact.

METHODS

We genotyped and immune phenotyped a cohort of 26 untreated Turkish BD subjects and 22 healthy donors, generated CRISPR-Cas9 ERAP1 KOs from HLA-B*51 ⁺ LCL, analysed the HLA class I-bound peptidome for peptide length differences and assessed immunogenicity of genome-edited cells in CD8 T cell co-culture systems.

RESULTS

Allele frequencies of ERAP1-Hap10 were similar to previous studies. There were frequency shifts between antigen-experienced and naïve CD8 T cell populations of carriers and non-carriers of ERAP1-Hap10 in an HLA-B*51 background. ERAP1 KO cells showed peptidomes with longer peptides above 9mer and significant differences in their ability to stimulate alloreactive CD8 T cells compared with wild-type control cells.

CONCLUSIONS

We demonstrate that hypoactive ERAP1 changes immunogenicity to CD8 T cells, mediated by an HLA class I peptidome with undertrimmed peptides. Naïve/effector CD8 T cell shifts in affected carriers provide evidence of the biological relevance of ERAP1-Hap10/HLA-B*51 at the cellular level and point to an HLA-B51-restricted process. Our findings suggest that variant ERAP1-Hap10 partakes in BD pathogenesis by generating HLA-B51-restricted peptides, causing a change in immunodominance of the ensuing CD8 T cell response.

Detecting Lesional Granulysin Levels for Rapid Diagnosis of Cytotoxic T lymphocyte-Mediated Bullous Skin Disorders

BACKGROUND

Bullous skin disorders are induced by different pathomechanisms and several are emergent, including Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN). Rapid diagnostic methods for SJS/TEN or cytotoxic T-lymphocyte (CTL)-mediated bullous disorders are crucial for early treatment. Granulysin, primarily expressed by CTLs, is a specific cytotoxic protein responsible for SJS/TEN and similar skin reactions.

OBJECTIVE

To assess granulysin levels in blister fluids to differentiate SJS/TEN and similar CTL-mediated bullous reactions from other autoimmune bullous disorders.

METHODS

Using ELISA, we measured granulysin in blister fluids from patients with bullous skin disorders, including SJS/TEN, erythema multiforme major, bullous fixed-drug eruption, bullous lupus erythematosus, paraneoplastic pemphigus, pemphigus vulgaris, bullous pemphigoid, purpura fulminans-related bullae, and hand-foot syndrome/hand-foot-skin reactions. We compared serum and blister granulysin levels in patients with SJS/TEN presenting varying severity, monitoring serial granulysin levels from acute to late stages.

RESULTS

Overall, 144 patients presenting with bullous skin disorders were enrolled. Blister granulysin levels (mean ± SD) in CTL-mediated disorders, including TEN (n = 28; 3938.7 ± 3475.7), SJS-TEN overlapping (n = 22; 1440.4 ± 1179.6), SJS (n = 14; 542.0 ± 503.2), erythema multiforme major (n = 7; 766.3 ± 1073.7), generalized bullous fixed-drug eruption (n = 10; 720.4 ± 858.3), and localized bullous fixed-drug eruption (n = 16; 69.0 ± 56.4), were significantly higher than in non-CTL-mediated bullous disorders (P < .0001), including bullous lupus erythematosus (n = 3; 22.7 ± 20.1), paraneoplastic pemphigus (n = 3; 20.3 ± 8.6), pemphigus vulgaris (n = 3; 4.4 ± 2.8), bullous pemphigoid (n = 18; 4.0 ± 2.7), purpura fulminans (n = 4; 5.9 ± 5.5), and hand-foot syndrome/hand-foot-skin reactions (n = 6; 4.6 ± 3.5). Blister granulysin levels correlated with clinical severity of SJS/TEN (P < .0001).

CONCLUSIONS

Determination of blister granulysin levels is a noninvasive and useful tool for rapid differential diagnosis of SJS/TEN and other similar CTL-mediated bullous skin disorders for treatment selection.