Lecture 1- introduction to the immune system Flashcards
what is the immune system for?
The immune system protects the individual against pathogens that try to invade and replicate within it and also from cancerous cells that divide in an uncontrolled fashion
how does the immune system cause disease?
autoimmune diseases and allergies
Cells of the immune system can be involved in causing disease – for example in autoimmunity when immune cells attack the body’s own cells or allergy when immune cells respond to environmental non-dangerous antigens.
how does manipulating the immune system protect people from disease
Vaccines are given to people to train their immune systems to protect against infections.
Many of the top selling drugs act on our immune system to reduce symptoms of autoimmunity or on cancer cells. Drugs classed as immunotherapy act on our immune system to repress it in the case of autoimmunity or enhance it in some cases of anti-cancer treatment.
how do we split the immune system up?
the innate and adaptive. The innate and adaptive immune system act together to protect the host
innate -
Acts quickly following infection
Found in all tissues especially at barrier sites
Limited specificity
Limited memory
adaptive -
Takes 5-10 days to get going
Mainly found in lymphoid organs
Specific for particular proteins or peptides
Long lived immune memory
what is the overview of initial response to infection?
Breach of tissue barrier
Activation of complement
Activation of local innate immune cells
Increased permeability of local blood vessel
Migration into tissues of more immune cells and plasma proteins
what are the differences between innate and adaptive immune cells?
innate -
Innate cells including macrophages, and dendritic cells live in tissues
Neutrophils and monocytes migrate in the blood
adaptive -
Conventional naïve B cells, CD4 and CD8 T cells migrate through the blood and secondary lymphoid organs
Memory T cells circulate through the blood and various tissues
how do cells communicate?
via small soluble molecules called cytokines
Innate cells that become aware of an infection make inflammatory cytokines that other innate and adaptive immune cells respond to.
how do B cells and T cells recognise different forms of antigen?
The BCR binds to native proteins/antigens
Antigens that cross-link surface BCR provide optimal B cell activation
No accessory cells required
T cells recognise processed antigen presented on MHC molecules on the surface of antigen presenting cells
CD8 T cells see short peptides in MHC class I molecules
CD4 T cells see longer peptides in MHC class II molecules
how do cells of the immune system work together to protect the host?
- Pathogens infect tissues and activate innate cells
- Activated DCs move to lymphoid organs carrying the pathogen
- DCs activate antigen specific CD4 and CD8 T cells
- CD4 T cells help B cells make antibody response
- T cells migrate out of the lymph node
- T cells migrate to infected tissues where they help innate cells kill the pathogen and antibodies aid clearance
how do receptors on the surface of cells allow immune cells to see what’s going on?
receptor binds ligand –> intracellular signalling –> Changes to cell function e.g. altered gene expression, cell movement, protein processing
Immune cells express an array of different receptors that act in concert to shape immune responses
how is the end just as important as the beginning?
Most T and B cells undergo apoptosis
A few cells remain as memory cells
These respond more quickly providing superior immune protection
Secondary responses are quicker and more effective than primary responses
how are Memory responses distinct from primary responses
Memory immune cells provide a more effective response than naïve immune cells because they are present at higher frequencies, located in barrier tissues and can remember the training they received in the primary response.
how are Pathogens are sensed by innate cells and information about them is passed down to adaptive immune cells
Pathogens, their products and the damage they cause are recognised by innate cells. These innate cells ‘pass’ this information onto cells of the adaptive immune system.
If the infection is mild, the innate immune cells may be able to clear the pathogen themselves. If not, they alert the adaptive immune cells.
