Introduction Flashcards
What is the immune system?
- provides defence/immunity against infection
- distinguishes between self and non-self, and reacts against non-self
- can recognise danger signals caused by damage to cells and tissues e.g. cancer, stroke
what is variolation?
- pus taken from a smallpox blister and introduced via a scratch into an uninfected person to confer protection
what are the 2 arms of the immune system?
innate
adaptive
what are the key features of the innate immune system?
- have this from birth
- broad specificity to recognise pathogens
- not affected by prior contact - no memory
- immediate/rapid response (hours)
what are the key features of the adaptive immune system?
- adapts to different pathogens that we are exposed to during our lifetime
- highly specific response to pathogens
- enhanced by prior contact - memory
- slow response (days-weeks)
what are the 4 main components of the innate immune system?
- Barriers (physical e.g. skin, chemical e.g. sebum)
- Soluble proteins (complement, interferons, defensins etc.)
- Local and systemic responses (inflammation, fever)
- Leukocytes (phagocytes, NK cells)
what are the main components/cells of the adaptive immune system? what are their main roles?
B and T lymphocytes
- B cells respond by secreting soluble antibodies (humoral immunity)
- T cells develop into cytotoxic T cells to kill infected host cells, or helper T cells to modulate the immune response (cell-mediated immunity)
- both B and T cells can develop into long-lived memory cells
where are leukocytes derived from?
Derived from pluripotent stem cells, which give rise to two main lineages, one for myeloid cells and one for lymphoid cells
How to B and T cells recognise infection?
they express specific antigen receptors called antibody receptors, or T cell receptors
how does the innate immune system recognise infection?
pattern recognition receptors (PRRs) on leukocytes that recognise pathogen-associated molecular patterns (PAMPs) found on pathogens
what are PAMPs/MAMPs?
PAMPs/MAMPs (e.g. LPS, peptidoglycan) – things that are commonly found on pathogens and not on host cells
- Unique to microbes
- Conserved
- Essential for microbe survival, so cannot be mutated
Main differences between innate and adaptive immunity receptors:
Innate:
- myeloid cells with broad specificity PRRs that recognise MAMPs
- NK cells recognise altered self
- PRRs expressed by all leukocytes of a particular cell type
- genes inherited in germline
- limited number
Adaptive:
- B and T cells have highly specific antigen receptors (antibody receptors and TCRs)
- clonally expressed
- genes assembled at random during development
- 10^9 specificites
what is the clonal selection hypothesis?
- When infected with a pathogen, a B cell will recognise the antigen and undergo clonal selection
- The B lymphocyte will divide and make clones with the same antibody receptor
- As they divide, they differentiate to plasma cells and begin to secrete large amounts of the antibodies
- Some of the B cells develop into long-lived memory cells to confer protection over a lifetime
- Any lymphocytes that recognise ‘self’ are deleted early in development
what must the immune system prevent whilst maximising its defences?
Immune system must maximise the host defence whilst minimising damage to host tissues
is the innate system good at avoiding damage to healthy host tissues?
- Small number of inherited PRRs recognise MAMPs unique to microbes
- Good at distinguishing between self and non-self
- Non-clonal activation
- Potential for collateral damage to self (immunopathology)
