topic 2 - the immune system Flashcards
cgp (topic 2C) 46 - 47
what triggers an immune response
foreign antigens
what are antigens
marker molecules (usually proteins) present on the surface of cells that can generate an immune response when detected by the body
what are antigens used by the immune system to identify
(1) pathogens
(2) abnormal body cells
(3) toxins/ cells from other individuals of the same species
what are the four main stages in the immune response
(1) phagocytes engulf pathogens
(2) phagocytes activate t-cells
(3) t-cells activate b-cells, which divide into plasma cells
(4) plasma cells make more antibodies to a specific antigen
what is a phagocyte
a type of blood cell that carries out phagocytosis
what is phagocytosis
the process by which a cell uses its plasma membrane to engulf pathogens
where are phagocytes found
in the blood and in tissues and are the first cells to respond to an immune system trigger inside the body
what’s an example of a phagocyte
macrophage
what is the first step to a phagocyte engulfing a pathogen
a phagocyte recognises the foreign antigens on a pathogen
what is the second step to a phagocyte engulfing a pathogen
the cytoplasm of the phagocyte moves round the pathogen, engulfing it
what is the third step to a phagocyte engulfing a pathogen
the pathogen is now contained in a phagocytic vacuole (a bubble) in the cytoplasm of the phagocyte
what is the fourth step to a phagocyte engulfing a pathogen
a lysosome (an organelle that contain enzymes called lysozymes) fuses with the phagocytic vacuole - the lysozymes break down the pathogen
what is the fifth step to a phagocyte engulfing a pathogen
the phagocyte then presents the pathogen’s antigens - it sticks the antigens on its surface to activate other immune system cells
what is a t-cell
otherwise known as a t-lymphocyte is a type of white blood cell
what activates the t-cell
when its receptor proteins on its surface bind to complementary antigens presented to it by pathogens
different t-cells respond in different ways, give an example
helper t-cells (tH cells) release chemical signals that activate and stimulate phagocytes and cytotoxic t-cells (tc cells), which kill abnormal and foreign cells
what are the two main types of t-cells
(1) cytotoxic t-cells which destroy infected cells
(2) helper t-cells which send signals that direct other immune cells to fight infection
what is a b-cell
otherwise known as b-lymphocytes is a type of white blood cell that is covered in antibodies which originates and matures in bone marrow
why do different b-cells bind to different shaped antigens
because each b-cell has a different shaped antibody on its membrane
what are the three steps to how b-cells divide into plasma cells
(1) when the antibody on the surface of a b-cell meets a complementary shaped antigen, it binds to it
(2) this, together with substances released from helper t-cells, activates the b-cell - this process is called clonal selection
(3) the activated b-cell divides into plasma cells
what other cell is identical to b-cells
plasma cells
what are monoclonal antibodies
antibodies specific to the antigen which are secreted by a single clone of a specific white blood cell (plasma cells)
what do monoclonal antibodies bind to, what does this form
they bind to antigens on the surface of the pathogen to form lots of antigen-antibody complexes
name seven structures on the antigen-antibody complex
(1) antigen
(2) variable regions
(3) hinge protein
(4) constant regions
(5) light chain
(6) disulfide bridges
(7) heavy chain
why do antibodies have two binding sites
so they can bind two pathogens at the same time - meaning that pathogens become clumped together (this is called agglutination)
phagocytes then bind to the antibodies and phagocytose many pathogens at once - this process leads to the destruction of pathogens carrying this antigen in the body
what are antibodies
proteins produced by the immune system in response to foreign substances - they are made up of chains of amino acids
what does the specificity of an antibody depend on
its variable regions - which form the antigen binding sites
what structure of an antibody is unique
its variable region with a unique tertiary structure (due to different amino acid sequences) that’s complementary to a specific antigen
what does the immune response split into
cellular and humoral
what is the cellular immune response
the t-cells and other immune system cells that interact with
what is the humoral immune response
b-cells, clonal selection and the production of monoclonal antibodies form the humoral response
what’s another word for an antibody
immunoglobulin
what is the primary response
when an antigen enters the body for the first time and activates the immune system
why is the primary response slow
because there aren’t many b-cells that can makes the antibody needed to bind to it
what do t-cells and b-cells produce after being exposed to an antigen, what do they do
memory cells - these memory cells remain in the body for a long time - memory t-cells remember the specific antigen and will recognise it a second time round - memory b-cells record the specific antibodies needed to bind the antigen
what is the secondary response
the second time the body is infected with the same pathogen, the immune system will produce a quicker, stronger immune response
how do b-cells and t-cells perform clonal selection in the secondary response
memory b-cells are activated to divide into plasma cells that produce the right antibody to the antigen - memory t-cells are activated and divide into the correct type of t-cells to kill the cell carrying the antigen - clonal selection is faster in this stage
