6.7 Response to infection Flashcards
what is the bodies first line of defence?
- surface of body (skin)
- lungs
- intestine
what is the body’s second line of defence?
inflammatory response
define inflammation
rapid, localised response of our tissues to damage
what triggers inflammation
when cells are damaged, they release ‘alarm’ chemicals including histamine
inflammatory response
what does histamine do?
- the smooth muscle of arterioles relaxes, increasing blood flow to that area.
- cells in the walls of capillaries draw away from one another (diapedesis), so that the capillaries become ‘leaky’, forming more tissue fluid than usual. This extra tissue fluid causes local swelling of the infected area. (oedema)
- sensory neurones become more sensitive
- complement proteins of plasma activated
inflammation
what is the effect of increased blood flow + leakage of plasma
- dilution and removal of toxins from invading microorganisms and from damaged cells
- more plasma + white blood cells
what two leucocytes are involved inflammatory response
what do each do
- neutrophils (short-lived) engulf bacteria identified by opsonins
- macrophages engulf lather debris and damaged cells
what are the two main steps necessary for phagocytosis
- must distinguish foreign cells from the body’s own cells
- engulfs and destroys foreign cell
what do neutrophils and macrophages have in common?
both are phagocytic leucocytes
what are the things that help pahocytes identify foreign cells (to engulf)
and where did they come from
complement proteins
histamines causes them to be activated in plasma
3 effects of complement proteins:
- attracting more phagoctyes to the site of infection
- binding to and forming pores in the surface membrane of foreign cells, leading to lysis of these cells
- binding to surface membranes of foreign cells thus aiding the attatchment of the surface membrane of a phagocyte to a foreign cell. These proteins are called opsinins.
describe phagocytosis
- phagocytic leucocyte detects presence of bacterium
- bacterium becomes attatched to receptor molecules on the cell surface membrane of leucocyte
- trapped bacterium engulfed in a food vacuole in the cytoplasm of leucocyte
- lysosomes in the cytoplasm fuse with the vacuole and discharge hydrolytic enzymes
- bacterium broken up into its constituent molecules and these are dispered into the cytoplasm (of leucocyte)
what are cytokines
a group of small proetins released by one type of cell that affects the behaviour of other cells
non specific still
what are interferons
what do they do
a group of cytokines called interferons are released by cells infected by viruses
these interferons bind to neighbouring healthy cells and trigger synthesis of antiviral proteins - as a reslut viral replication is slowed or halted.
what are the two types of leucocyte that are specific
lymphoctes:
- B lymphocytes (B cells) - humoral
- T lymphotes (T cells) - cell-mediated
bees make you laugh… humoural
where do both lymphocytes come from and where do they mature
both are produced by multipotent stem cells in marrow of some bones, t cells leave bone marrow to mature in the thymus gland whereas b cells stay in the bone marrow to mature.
define antigen
what molecules classify
any molecule that can stimulate an immune response.
small molecules like amino acids and sugars do not cause an immune response
large molecules like glycoproteins, glycolipids, proteins do.
The cell surface surface of the cell is coated in antigens
why are glycoproteins useful
they are highly variable and help to identify cells so are called markers
define MHC
Major Histocompatability complex (MHC) protiens
Glycoproteins found on the cell surface membrane of a cell membrane of a cell that are unique to that individual. In humans, these are often called human leucocyte associated antigens (HLA).
**They help identify cells **
are types of antigen
what do B and T cells have on their surface that allow them to recognise cells
antigen receptor molecules
( molecules that are complementary to very specific antigens )
what is the consequence of the antigen-receptors on B/T cells being complementary to a specific antigen?
each lymphoctye can only recognise one type of antigen
what are antibodies
the antigen receptor molecules of a B cell that are released.
what are the two most common antibodies?
what are they
igG
igM
they are a type of protein, immunoglobin (ig)
describe the structure of igG
four polypeptides linked by disulfide bridges to form a Y shape, two cghains are large (the heavy chains) and two are small (light chains)
define self-antigen
and why do they not trigger immune response against themselves
a glycoprotein on the cell surface membrane of one of the body’s own cells.
(The ability of this glycoprotein to cause an immune response is reduced by the body destroying any randomly produced lymphocytes with a complementary antigen-receptor. )
what is the humoral response
response involving the release of antibodies by B-cells.
outline the humoral response
- antigen to antibody on the B cell surface membrane
- antigen taken up by exocytosis and is expressed on the cell surface membrane at the MHC protien
- Meanwhile.. macrophages engulf antigens by endocytosis and then express this antigen on their MHC proteins on the cell surface membrane = antigen presentation
- T cell binds (briefly) to macrophage that presents an antigen and is activated- it is now an activated T helper cell
- activated T helper cell now binds to B cell with the same antigen expressed-immediately the B cell is activated = activated B cell
- activated B divides rapidly forming a clone of plasma cells - each containg lots of rER now mass producing antibody molcules that are secreted by exocytosis
- (some activated B cells and T cells surviuve in the body as memory cells, and are able to initiate a more speedy response in the event of re-infections
antibodies overcome antigen eg by neutralising it by causing clumping together of cells to aid engulfing by other macrophages
outline the cell mediated response
- complementary T cell binds to macrophae presenting complementary antigen = activated T helper cell
- T helper cells release cytokines that stimulate T helper cell to divide repeatedly to form clones
clone could be three types of T helper cell
3 types of T cell (from clone)
- T killer cells- destroy body cells infected by virus or other cells carrying for example TAA (tumor associated antigens)
- T helper cells- release cytokines that stimulate the production of B cells
- Memory cells- remain in the body and bring about the secondary response (re-infection).
contrast primary and secondary immune reponse (re-infection)
secondary is
- faster rate of antibody production
- shorter time lag between exposure an antibody production
- higher concentration of antibodies
- antibdoy level remains higher after the secondary response
- pathogen usually destroyed before any symptoms
similarities between passive and active immunity
- both involve antibodies
- both can be natural or arificial
give examples of passive and active immunity
passive natural: antibodies in breast milk
passive artificial: anti-venom
active natural: humoral response to infection
active artificial: vaccination
contrast passive and active immunity
passive:
- no memory cells and antibodies not replaced when broken down= short term
- immediate
- antibodies from external source
- direct contact with antigen not necessary
active:
- memory cells produced = long-term memory
- time lag
- lymphocytes produce antibodies
- direct contact with the antigen necessary
explain the principles of vaccination
- vaccine contains dead/inactive form of a pathogen or antigen
- triggers primary immune reponse
- memory cells are produced and remian in the bloodstream so secondary response is rapid and produce higher conc of antibodies
- pathogen is destroyed before it causes symptoms.
what is herd immunity?
vaccinating 80-90% of population reduces available carriers of the pathogen to control disease transmission
protects individuls who have not been vaccinated eg: those with a weak immune system.
