Monocyte Pathology in Ankylosing Spondylitis

Thesis

Background

Ankylosing spondylitis (AS) is a genetically predisposed, immune-mediated inflammatory disease characterised by hyperactivity of monocytes and T helper 17 (Th17) cells. Intrleukin (IL)-1β and IL-23 produced by myeloid cells drive the pathogenic Th17 response. Although genetic association studies have identified numerous AS-risk genes, relatively few have been functionally linked to monocyte pathology. Consequently, the mechanisms by which monocytes become activated in AS remain incompletely understood. My DPhil research investigated three interconnected mechanisms in AS pathogenesis: (1) trained immunity (TI) in monocytes from AS patients and their crosstalk with T cells, (2) T cell-instructed IL-1β production in human myeloid cells, and (3) ERAP1-mediated regulation of the IL-23/Th17 axis, a key pathway associated with AS genetic susceptibility.

Methods

Primary peripheral blood mononuclear cells (PBMCs) from HLA-B27-positive AS patients (n=97), healthy controls (n=17), and leukocyte cones (n=56) were used in this study. Small interfering RNAs (siRNAs), neutralising antibodies, and inhibitors were used to study the function of genes. Knockdown efficiency was validated by quantitative PCR (qPCR) and Western blotting. Flow cytometry, enzyme-linked immunosorbent assay (ELISA), caspase-1 activity assay, and Western blotting were used to quantify the production of proteins.

Results

I identified a monocyte subset that is expanded in patients with AS and exhibits transcriptional and functional (hyper-responsiveness to LPS stimulation) features of TI. Both this trained monocyte subset in AS and β-glucan-trained monocyte-derived macrophages from healthy donors are hyper-responsive to T cell-induced activation. Additionally, T cell-activated monocytes can act back on T cells to promote Th17 responses. A subsequent siRNA screening of AS risk genes identified ZC3H12C, ERN1, and IL1R1 as key regulators of T cell-induced monocyte activation. Additionally, my findings show that activated CD4+ T cells are capable of inducing IL-1β production by primary human myeloid cells through the upregulation of pro-IL-1β by TNF-α, CD40L, and IFN-γ, followed by caspase-1-mediated cleavage. Lastly, ERAP1 modulates the pathogenic IL-23/IL-17 axis while preserving IFN-γ-mediated immunity.

Conclusions

This study demonstrates for the first time the presence of trained immunity in monocytes from patients with AS and highlights the pivotal role of monocyte-T cell interactions in AS pathology. Mechanistic studies identified the contribution of genetic risk factors, myeloid hyperactivation, and T cell-driven inflammation to the pathogenesis of AS, thereby providing new insights into the development of novel therapeutics for T cell-driven autoimmune diseases.

Authors: Zhao, J

• DOI: 10.5287/ora-w4kmg2rwe
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: T-cells; myeloid cells; innate immunity; ankylosing spondylitis
• Subjects: Molecular immunology