L25 - Cytokines in RA Flashcards
What innate immunity cells are found in the joints of RA patients?
Macrophages, NK cells, dendritic cells, neutrophils, mast cells
What are some roles of cytokines?
Neuroendorcine system
Immune regulation
Cancer cell biology
What are some roles of IL6
- Local Leukocyte and osteoclast activation
- B cell differentiation
- Systemic Effects
What are some roles of IL1?
- local leukocyte, fibroblast and endothelial activation
- systemic effects
What are some of the cellular sources of TNF?
Kupffer cells Macrophages/Neutrophils/Eosinophils T lymphocytes/NK cells Astrocytes Langerhans cells Keratinocytes/Fibroblasts Smooth Muscle
What are some cellular biological activities of TNF (not related to RA)?
- cytotoxic to some tumour cells
- growth promoter to other tumour cells
- induce insulin resistance
- Na+ sequestration which affects Na+ concentration in excitable cells (cardiac, skeletal, nerves)
What are some agents that stimulate TNF release?
bacterial toxins, viruses, microbacteria, fungi, parasites, complement activation products, antigen-antibody complexes, cytokines, physical agents (hypoxia, trauma, irradiation)
NOT ACPA
List the types of TNF and their properties
tmTNF -transmembrane-associated -26kD -converted to soluble form via TACE -tmTNF form is active in a paracrine fashion sTNF -soluble form -17kD -active as a trimer non-covalently bonded -short half life
What are the chronic low dose symptoms associated with RA?
Weight loss
Subendocardial inflammation
Acute phase protein release
Endothelial activation
What causes the long-lasting effects of TNF (which generally has a short half-life)?
- Activation of other factors such as hormones (which then travel and affect other areas)
- Chronic production of TNF from chronic inflammation
Where are TNFRIIs expressed?
enothelial and haematopoetic cells (except RBCs!)
What is some of the effects of TNF-a in RA synovium?
- Induces production of IL1. IL6 and IL8
- stimulates synovial FBs to express adhesion molecules which attract leukocytes
- stimulates synoviual macrophages and firborgen metalloproteinase synthesis
- T cells in synovium lymophcyte aggregates exculsively express TNF2
What are some of the effects of TNF-a on RA cartilage?
- inhibits synthesis of chondrocyte proteoglycan
- increases metalloproteinase expression by chondrocytes and synovial fibroblasts (destruction)
What are some of the effects of TNF-a on RA bone?
Stimulates osteoclastogenesis dn their activation (directly and via RANKL)
inhibits osteoblasts
What are some of the effects of methotrexate?
Reduces inflammatory and immune cell and recuitment to joint
Reduces expression of adhesion moelcules and MMPs
Inhibits T cell activities (esp T cell proliferation and IFN-y production)
Anti-inflam effects mediated by (adenosine, dihydrofolate reductase inhibitor, polyamine reduction)
increases apoptosis and slows turnover of rapidly diving cells
What are the predominant immune cell type in synovial fluid and in the pannus?
Synovial fluid: neutrophil
Pannus: macrophages and lymphocytes
How do the 2 different TNFR contribute to biological complexity of RA?
- two different pathways
- different binding kinetics
- reverse signalling
- variable actions depending on metaoblic activity of target cell
What are the common TNF inhibitors?
- Infliximab – mouse/human chimeric monoclonal anti-TNF antibody of IgG isotope, first TNF inhibitor
- Etanercept is a fusion protein of TNFR2 (p75) and the Fc region of human IgG1 – second TNF inibitor
- Adalimumab and golimumab are fully human IgG1 monoclonal anti-TNF antibodies
- Certolizumab is a PEGylated Fab’ fragment of a humanised IgG1 monoclonal anti-TNF antibody
What are the results of TNF-inhibitor trials in vivo (humans)?
• reduces concentration of IL1, TNF, GM-CSF, IL6 in synovial fluid or serum
• Levels of inflammatory cytokines eg. IL6 drop within hours
• Dramatic improvement in pain stiffness and fatigue
• Normal Treg functional status restored
• Haematologic paramters (Hb, ESR, CRP) normalised
Decrease metalloproteinases (increase OPG)
Reduce neutrophil migration to joint
• Early human trials showed partial extinction of the improvement between doses (duration of improvement decreased with sequential doses)
o ? Due to immunogenicity leading to rapid clearance and/or inactivation of the drug, thus requiring dosage escalation (anti-TNF Abs found)
o ? TNF-BPs – role in clearance
Chimeric Abs are generally more immunogenic than humanised or human anitbodies
• Efficacy much improved with methotrexate co-administered
o ? T cell effects? blocks anti-TNFI Ab
• Longer trials confirmed reduction in damage to cartilage and bone with TNFI/Methotrexate compared to methotrexate alone
Why aren’t TNFIs not used univresally?
Cost
Risk of infection and malignancy (TNF key player in immune response)
Inability to predict severity of disease progression in early RA patients
