introduction to immunology Flashcards
innate immune system
immune system provides protection within minutes of an assault
epithelial defences
pathogen associated molecular patterns
the complement system
other innate responses
epithelial defences
skin
>salt in sweat
> PH
mucus-producing epithelia
acidic enviroments
>stomach
>urogenital tract
cannot attach to outer skin layer because composed dead keratinocytes , keratin , ceramides and cholesterol
apart from staph.epidermis
skin between PH 3-5 -> inhibits bacterial growth
mucus covering replaced several times each day
acidic environment prevents bacterial growth
mucociliary escalator
cilia beat and move mucus up towards the epiglottis and it is swallowed or expelled from airways
PAMPS
the innate immune system recognises key features common to pathogens but absent from the host
these are pathogen associated molecular patterns (PAMPS)
formulated methionine (the first amino acids in all bacterial proteins)
lipopolysaccharides of gram negative bacteria
teichoic acids of gram positive bacteria
complement cascade
enhances the ability of antibodies and phagocytes to clear microbes and damaged cells.
promotes inflammation
attacks the pathogens plasma membrane
numerous complement proteins involved acting in a cascade
classical - antibodies involved
alternative - antibodies not required
other innate immune responses
phagocytosis - invader engulfed by neutrophils or macrophages
inflammation - dilation of local blood vessels and recruitment of lymphocytes
interferons - mediate cell shutdown in response to viral double stranded RNA
natural killer cells - induce death of infected cells by apoptosis
innate immunity
acute phase response , not pathogen specific
initial response to tissue injury
controls pathogenic microbes until the adaptive immune response is activated
physical/chemical barriers
recruits immune cells to sites of infection
> myeloid cells are responsible for innate response
stimulates adaptive response
adaptive immune system
the innate and adaptive systems work together to fight infection but have important differences
the adaptive response is :
pathogen - specific (and so more effective)
long-lasting - after first exposure to an antigen , the second exposure induces a very rapid and specific response - anamnestic response.
antigen is any molecule which stimulates the immune system
the role of lymphocytes
lymphocytes are responsible for the adaptive response
B cells
>come from bone marrow
>produce antibodies
> effects are systemic
T cells
>come from thymus
>stimulated by MHC on antigen-presenting cells
> effects are localised
Antibodies
soluble proteins produced by plasma cells (type of B cell)
found in peripheral blood, tears , saliva
neutralises viruses or mark microbes for destruction by phagocytosis or complement
basic structure consisting of pairs of heavy (H) and light (L) chains
Antibody classes
Ig M- secreted antibody in primary response
Ig G - major class of blood antibody in secondary response
Ig A - found in secretions (saliva , tears , etc)
Ig E- triggers histamine response , allergy response
Ig D - may play a role in respiratory immune defence
antibodies provide long term protection (memory cells )
T cells and their receptors
unlike B cells , T cells only react to antigen when presented to them by an antigen presenting cell
when an antigen presenting cell breaks up a pathogen , fragments of the antigen are carried to the cell surface
major histocompatibility complex on the surface of the antigen presenting cell display fragments to T cells
T cells recognise the antigen by binding to them using T cell receptors
T cells induce death in infected cells
T cells act by direct contact
TCR recognition of antigen on MHC can cause cell killing by different mechanisms
most involve activating a suicide program(apoptosis) in the target
B and T cells working together - IgE and allergy
type I hypersensitivity is an allergic reaction provoked by re-exposure to a specific type of antigen called an allergen
allergen stimulates T cells to produce cytokines which activate B cells
B cells are stimulated to produce IgE antibodies specific to the allergen
IgE binds to mast cells and basophils
these cells release contents such as histamines causing rash etc
