T and B cells, cytokines and dendritic cells Flashcards
How do cells of the immune system communicate between themselves, and with other non-immune cells?
- Cell-cell contact (signalling through receptor -ligand interactions between membranes of different cells, (eg MHC and TcR)
- Secretion of soluble factors that initiate responses and signals by binding to specific receptors (e.g. cytokines)
Define cytokines.
Small polypeptides, around 25,000 Mr released by cells in response to an activating stimulus. Can have autocrine, paracrine and endocrine (latter limited by ability to enter circulation and half-life) actions.
Define chemokines.
A class of cytokine that has chemoattractant properties, ie induces cells to migrate towards the source.
Define interleukins.
Cytokines secreted by leucocytes
Identify the main groups if chemokines. Why were these groups get named the way they did ?
- CC (which bind to receptors CCR1 to 9)
- CXC (which bind to CXCR1 to 5)
Named due to spacing of cysteine residues close to amino terminus (two N-terminal cysteines of CXC chemokines separated by one amino acid VS two adjacent cysteines near their amino terminus).
Describe the main features of IL-8, including source, receptors, target cells, major effects, and type of cytokine.
- CXC Chemokine
- Source: Monocytes, macrophages, fibroblasts, keratinocytes, endothelial cells
- Receptors: CXCR1 and CXCR2
- Target cells: Neutrophils and naive T cells
- Major effects: Mobilises, activates and degranulates neutrophils + Angiogenesis + induces chemotaxis in target cells, causing them to migrate toward the site of infection and induces phagocytosis once they have arrived
Describe the function of Interleukin 2. How is it secreted ?
Activates and grows T cells (growth factor for other T cells)
Secreted by T cells
Describe the function of Interleukin 4.
Activates and grows B cells + switches them to produce IgE (important in allergy)
Describe the function of Interferon gamma.
Activates strong cell mediated responses (e.g. Cytotoxic T lymphocytes) + Causes upregulation of MHC class 1 and 2.
Describe the function of TNF-alpha. How is it secreted ?
Pro-inflammatory (activates vascular endothelium and increases vascular permeability)
Secreted by T cells
What treatment is there to dampen down pro-inflammatory response of TNF (e.g. in rhumatoid arthritis) ?
Inflixamab
Do cells produce one type of cytokine only or more than one ?
A cell will tend to produce different cytokines with different effects on cells
How do neutrophils access infection sites ?
Neutrophils access infection sites by diapedesis
What is a problem associated with TNF alpha release ?
Its release normally triggers local protection (by allowing lymphocytes to travel thanks to decreased vascular permability, but can induce systemic shock –> if overproduction of TNF-alpha)
Notably including systemic oedema, decreased blood volume, hypoproteinemia, neutropenia followed by neutrophillia, collapse of vessels. May result in death
Describe the process through which Interleukin 2 induces proliferation of T cells.
- Naive T cells express the low affinity IL-2 receptor
- Activated T-cells express the high affinity IL-2 receptor and secrete IL-2
- Binding of IL-2 to high affinity receptor sends a signal to the T cell
- The signal sent from IL-2 receptor induces T cell proliferation
