The Science of Rheumatoid Arthritis Flashcards Preview

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Flashcards in The Science of Rheumatoid Arthritis Deck (40)
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What are the function of the synovium?

-Maintenance of intact tissue surface
-Lubrication of cartilage
-Control of synovial fluid volume and composition (hyaluronan, lubricin)
-Nutrition of chondrocytes within joints


Describe the joint affected by rheumatoid arthritis.

-Erosion into corner of bone
-Thinning of cartilage
-Inflammed synovium spreading across joint surface
-Inflammed tendon sheath


What is rheumatoid arthritis?

Rheumatoid arthritis is a chronic symmetric polyarticular inflammatory joint disease, which primarily affects the small joints of the hands and feet


What is rheumatoid synovitis (pannus) characterised by?

Inflammatory cell infiltration, synoviocyte proliferation and neoangiogenesis


In rheumatoid arthritis, what does the synovial fluid in the joint cavity contain?

Neutrophils, particularly during acute flares


What does the synovial pannus cause?

Bone and cartilage destruction (deformities)


When can evidence of autoimmunity be present?

Evidence of autoimmunity can be present in RA many years before the onset of clinical arthritis


What autoantibodies are commonly associated with RA?

-Rheumatoid factors
-Anti-citrullinated protein


What do autoantibodies recognise in RA?

Either joint antigens such as type II collagen or systemic antigens such as glucose phosphate isomerase


How can autoantibodies contribute to inflammation?

Through several mechanisms including activation of complement


What autoantibodies are produced in seropositive RA?

-Rheumatoid factor
-Anti-cirtullinated protein antibody (ACPA)


What do diagnostic anti-CCP assays recognise in seropositive antibody production?

-Citrullinated self-proteins


What seropositive RA patients have a poorer prognosis?

Patients with ACPA disease


What is rheumatoid factor?

An auto-antibody to self IgG Fc


What genetic factors contribute to RA?

-Concordance rates 15-30% in monozygotic twins and 5% in dizygotic twins
-Association with HLA-DRB1 locus (HLA-DR4 serotype)
-Other genetic associations including polymorphisms in PTPN22, CTLA4, c-REL etc. aggregate functionally with immune regulation


What environmental factors contribute to RA?

-Smoking and bronchial stress (exposure to silica)
-Infectious agents (viruses, E.coli, mycoplasma, periodontal disease, microbiome)


What would repeated environmental insults in a genetically susceptible individual lead to?

-Formation of immune complexes and rheumatoid factor (high-affinity autoAb against the Fc portion of Ig)
-Altered citrullination of proteins and breakdown of tolerance, with resulting ACPA response


What is citrullination?

-(Or deimination) is the conversion of the amino acid arginine in a protein into the amino acid citrulline.
-Enzymes called peptidylarginine deiminases (PADs) replace the primary ketimine group (=NH) by a ketone group (=O).


Why does synovitis occur in RA?

-Intimal lining hyperplasia and sublining infiltration (migration) with mononuclear cells, especially CD4 + T cells, macrophages, and B cells
-Lining FLS proliferate, become activated and “aggressive”
-Macrophages in lining activated
-Lymphocytes can either diffusely infiltrate the sublining or form lymphoid aggregates with germinal centres
-Sublining CD4+ T cells mainly display the memory cell phenotype
-Synovial B cells and plasma cells exhibit evidence of antigen-driven maturation and antibody production
-DCs can present antigens to T cells in synovial germinal centres
-Neoangiogenesis induced by local hypoxic conditions and cytokines
-Insufficient lymphangiogenesis limits cellular egress
-Neutrophils in synovial fluid


What is synovitis?

Inflammation of the synovium


What is the pathogenesis of RA?

-Villous hyperplasia
-Infiltration of T cells, B cells,
-Macrophages and plasma cells
-Intimal cell proliferation (fibroblasts)
-Production of cytokines and proteases
-Increased vascularity
-Self-amplifying process


What role do T cells play in RA?

Relatively low levels of T cell cytokines are present in RA synovium

Shift from homeostasis to inflammation
-T-cell cytokines, such as IFN- γ and IL-17, are produced by Th1 cells or Th17 cells
-Regulatory T cell function, which suppresses activation of other T cells, is reduced

T cell mediated B cell activation

Direct cell to cell contact with macrophages


How can T cells be targeted in RA?

-T-cell depleting strategies have limited efficacy
-Abatacept (fusion protein CTLA4-IgG1 Fc that blocks T-cell costimulation) is efficacious in RA


What role do B cells play in RA?

-Synovial B cells are mainly localised in T cell B cell aggregates (ectopic lymphoid follicles)
-Pathogenic role for CD20+ B cells is confirmed by the efficacy of rituximab
-Plasma cells are widely distributed and are not targeted by anti-CD20 antibodies
-Role of B cells goes beyond production of autoAb (autoantigen presentation, cytokines IL-6 and TNFa)


What are abundant in RA?

Macrophage and fibroblast cytokines


What are macrophages activated by?

TLRs and NLRs


What perpetuates synovial inflammation?

Cytokine networks including TNF-α, IL-6, IL-1, IL-15, IL-18, IL-23


What do the macrophages and fibroblasts produce?

Chemokines that recruit inflammatory cells into the joints


What anti-inflammatory response does the synovium have?

Anti-inflammatory cytokines such as IL-10 are produced in rheumatoid synovium but in amounts insufficient to offset proinflammatory cytokines


What do inflammatory cytokines do?

-Induce expression of endothelial-cell adhesion molecules
-Activate synovial fibroblasts, chondrocytes, osteoclasts
-Promote angiogenesis
-Suppress T-regs
-Activate leukocytes
-Promtoe autoAb production