Third line of defence Flashcards
what initiates the third line of defence
the presentation of an antigen with MHC II markers
what is the role of dendritic cells/macrophages in the third line of defence
they engulf and digest a pathogen, presenting the antigens of the pathogens on their own MHC II markers, they then travel to the lymph node where they encounter T helper cells
T helper cells are aka
T lymphocytes, CD4+ cells
when a macrophage/dendritic cell encounters a t helper cell, rarely anything happens, why…
T helper cells all have unique T-cell receptorrs on there surface, rarely anyything happens because the macrophage/dendritic cell and t-helper cell dont have matching antigens
what happens when the dendritic cell/macrophage encounters the specific T-helper cells
they bind and the t-helper cell becomes avtivated, causes the naive t-cells to undergo colonal selection and cytokines are released
what are the two processes of the third line of defence
humoural response annd cell mediated response
cell mediated response
uses T cells to target antigens, effective against intracellular pathogens
when a helper t-cell secretes cytokines after binding to the macrophage/dendrites, what does this cause
the cytokines stimulates the helper t-cells to unergo clonal expansion - rapid miotic division (all with the have same receptors as original) and differentiation into cytotoxic t-cells and t memory cells
what do the cytotoxic cells do once produced/differentiated
they spread throughout the body and identify self cells in the body that have foreugn antigens rgat fit their t-cell receptors, presented on its MHC I marker, they tthen release a death lignand that induces apoptosis in the infected in the cell
humoral immunity
effective against extracellular pathogens, neutralising and destroying them
structture of B lymphocytes
covered in antibodies (immunoglobulins) and contain MHC II markers
where are B lymphocytes found
reside in the lymph nodes in high numbers and travel around the blood strea,
what activates a B lymphocyte
comes into contact with a pathogen, dendritic cell/acrophage or free virus particles that have the antigen complementary to the shape of the antigen binding site on its cell receptors
once a b lymphocyte encounters dendritic cell/macrophage or free virus particles that have the antigen complementary to the shape of the antigen binding site on its cell receptors
Th b lymohcyte will engulf the pathogen by phagocytosis and present the antigens of the pathogen on its own MHC II markers, b lmphocyte is said to be selected
once the b lymphocyte has been selected
the t helper cell with the complementary recpetor to the antigen will recognise the selected b cell and secrete cytokines which cause the b-lymphocyte to undergo clonaal expansion and differentiation, producing b memeory cells and plasma cells
plasmaaa cells
differentiated clones of the the selected b lymphocyte, they secrete antibodies into the blood to defend against the specific pathogen, short lived cells
b memeory cells
used for fast response to future exposure of the same pathogen, long lasting
what are the five actions of antibodies
neutralisationn, aggultination, immobilisation, opsonisation and activation of complement proteins NAIOC
neutralisation
block the sites of pathogens tthat are used to attack host cells
agglutination
can bind with antigens on two seperate pathogens making it easier for phagocytes to recognise the pathogen as forgein and destroy it
immobilisation
restrict the movement of pathogens around the body through the formation of large antigen-antibody complexes
opsonisation
bind directly to the surface of the pathogen to make it easier for phagocytosis to take place
what is an antibody
a specific form of an immunoglobu;in, a protein found on the surface of a b cell, specific in nature
