cell recognition + immune system + antibodies

what is a defence mechanism?

range of defences of human body to protect itself from pathogens

what are the 2 types of defence mechanisms?

non-specific, specific

2 examples of a non-specific defence mechanism?

physical barrier e.g. skin, phagocytosis

2 examples of a specific defence mechanism?

cell-mediated response- T lymphocytes, humoral response- B lymphocytes

what is a non-specific response

a type of defence mechanism which is immediate and the same for all pathogens

what is a specific response?

a type of defence mechanism which is slower, longer lasting and specific to each pathogen

what do lymphocytes do, and if they couldn’t do this, what would happen?

defend the body from invasion by foreign material by distinguishing between self and non-self cells. if they couldn’t do this, lymphocytes would destroy the organism’s own tissues

what are self cells?

the bodys own cells and molecules

what are non-self cells?

cells or molecules that are foreign

why are proteins the most important molecule in the action of lymphocytes?

allow the immune system to identify pathogens- antigens e.g. HIV, non-self material e.g. cells from other organisms of same species, toxins produced by pathogens, abnormal body cells e.g. cancer

what does pathogen identification do to people with organ or tissue transplants?

immune system recognises transplanted tissue as non-self and attacks it

what are 2 solutions for the immune system attacking transplanted organs/tissue?

tissue matching, immunosuppressant drugs

how do lymphocytes recognise cells belonging to the body in a foetus (long answer)

• 10 million different lymphocytes, each recognise different chemical shape

• infection of foetus rare- protected from outside by mother, incl placenta

• in foetus, lymphocytes constantly colliding w other cells, mostly collide w self material

• some lymphocytes have receptors that exactly fit body’s own cells

• these lymphocytes die/are suppressed.

• remaining lymphocytes = ones that might fit non-self material, therefore only respond to foreign material

how do lymphocytes recognise cells belonging to the body in an adult

• lymphocytes produced in bone marrow initially only encounter self-antigens

• lymphocytes that show immune response to self-antigens = programmed cell death, apoptosis, before can differentiate into mature lymphocytes

• only lymphocytes that dont react to self-antigens survive and circulate in blood, where can respond to foreign antigens

is phagocytosis a specific or non-specific defence mechanism?

non specific

explain the process of phagocytosis.

• chemical products of pathogen/dead, damaged, abnormal cells act as attractants, phagocytes move towards pathogen e.g. bacterium.

• receptors on CSM of phagocyte bind to antigen on pathogen CSM

• engulf pathogen to form phagosome

• lysosomes move towards vesicle and fuse with it

• lysozymes destroy pathogen- hydrolyse cell walls, break down larger insoluble molecules into smaller soluble ones

• soluble products from breakdown of pathogen absorbed into cytoplasm of phagocyte

what is an antigen

any part of an organism or substance that is recognised as non-self (foreign) by the immune system and stimulates an immune response.

what are antigens usually in the form of?

proteins that are part of the cell surface membranes or cell walls of invading cells or abnormal body cells like cancer

what does the presence of an antigen trigger in the body?

production of an antibody as part of the body’s defence system

where are lymphocytes produced and by what?

by stem cells in the bone marrow

where do B lymphocytes mature?

bone marrow

what are B lymphocytes associated with?

humoral immunity, immunity involving antibodies that are present in body fluids e.g. plasma

Where do T lymphocytes mature

thymus gland

what are T lymphocytes associated with ?

cell mediated immunity, immunity involving body cells

what to T lymphocytes respond to?

antigens that are presented on a body cell

T lymphocytes can distinguish invader cells from normal cells how? (4 ways)

phagocytes that have engulfed + hydrolysed a pathogen display its antigens on their CSM

body cells invaded by virus present some of the viral antigens on their own CSM

transplanted cells from individuals of same species have different antigens on CSM

cancer cells different from normal body cells, present antigens on CSM

antigen presenting cells

present antigens of other cells on their own cell surface membrane

stages in response of T lymphocytes to infection by a pathogen (label)

1. pathogens invade body cells or are taken in by phagocytes

2. phagocyte places antigens from the pathogen on its CSM

3. receptors on specific helper T cell fit exactly onto these antigens

4. this attachment activates T cell to divide rapidly by mitosis and form a clone of genetically identical cells

5. cloned T cells perform 4 different functions

what are the 4 things the cloned, genetically identical T cells can do? (response of T lymphocytes to infection by pathogen)

1. develop into memory cells that enable a rapid response to future infections by the same pathogen

2. stimulate phagocytes to engulf pathogens by phagocytosis

3. stimulate B cells to divide and secrete their antibody

4. activate cytotoxic T cells.

how do cytotoxic T cells kill infected cells?

produce a protein called perforin that makes holes in the CSM. cell membrane freely permeable to all substances, and cell dies

the action of T cells is most effective against which type of cell and why?

viruses because replicate inside of cells

use living cells to replicate, so sacrificing body cells prevents them from multiplying and infecting more cells

process of antigen presentation (part 2 of cell mediated response)

• after phagocytosis, phagocytes display antigens of foreign cells on their cell surface, becoming antigen presenting cells.

• T helper cells only respond to antigens present on other cells

• Each T helper cell has a specific receptor to different types of antigen

• T helper cell binds to antigen on the antigen on the phagocyte, activating it to divide rapidly by mitosis, making clones of the required T helper cell

• called clonal selection

what is the cascade effect? (3rd part of cell mediated response)

clonal T helper cells produce cytokines which stimulate more responses: more phagocytosis, stimulation of division of B cells for antibody production, production of memory T cells, activation of cytotoxic T cells

what are antigens/what do they do?

recognised as non-self (foreign) by the immune system and stimulates an immune response

what 3 things can antigens be derived from?

pathogens, transplanted cells, cancer

what does the presence of an antigen trigger?

production of antibodies or other specific immune responses

what are granulocytes?

type of immune cell, has granules with enzymes that are released during infection, allergic reactions, asthma

are granulocytes specific or non-specific?

non-specific

what are neutrophils?

a type of granulocyte/phagocytic wbc, kills bacteria through phagocytosis

what are esinophils?

type of granulocyte ,releases toxins (enzymes) from granules to kill pathogens

what are basophils?

type of granulocyte, functions in allergic reactions

what are agranulocytes

a type of immune cell (has no granules)

are agranulocytes specific or non specific?

mostly specific

what are monocytes?

agranulocytes- enter tissue + become larger, turning into macrophages.

destroy old, damaged and dead cells in the body

what are lymphocytes

agranulocytes. T lymphocytes =cell mediated immunity, B lymphocytes = humoral immunity/antibody production

what are plasma cells involved with?

primary immune response (first time being infected by a pathogen)

what do plasma cells secrete?

antibodies

how long do plasma cells survive for?

a few days

how fast is the response for plasma cells?

slow- the person will get ill before the pathogen is killed

what are memory cells involved in?

secondary immune response

where do memory cells circulate?

blood and tissue fluid

when memory cells encounter the antigen from the primary response, what happens?

they divide rapidly

how fast is the response of memory cells

rapid, the person will not get ill

mechanism of the B cell response (humoral immunity-long answer)

surface antigen of an invading pathogen is taken in by a B cell. the B cell processes the pathogens and presents them on its surface. helper T cells receptors bind to the processed antigens on the B cell, activating it. The B cell is activated to divide by mitosis to give a clone of the plasma B cells. these cloned plasma cells produce and secrete the specific antibody that fits the antigen on the pathogens surface. the antibody binds to antigens on the pathogen and destroys them. some B cells develop into memory cells. these can respond to future infections by the same pathogen by dividing rapidly and developing into plasma cells

in humoral immunity, how are pathogens identified?

B cells become antigen presenting cells

in humoral immunity, how are pathogens killed?

antibodies

in humoral immunity, how do cells divide once they are stimulated?

divide by mitosis into plasma B cells or memory B cells

in cell-mediated immunity, how are pathogens identified?

antigens engulfed and presented on the surface of white blood cells

in cell-mediated immunity, how are pathogens killed?

cytotoxic T cells, phagocytosis

in cell-mediated immunity, how do cells divide once they are stimulated?

T cells divide by mitosis into different types of T cells e.g. cytotoxic, helper, memory

how do antibodies work? 5

agglutination- clumps antigens and pathogens together which marks them out for phagocytosis.

cause bacteria to stick together = easier for phagocyte to engulf them.

antibody can bind to more than 1 antigen.

antibodies then act as markers to stimulate phagocytosis.

explain what is an antigen-antibody reaction

each antibody complementary to specific antigens on CSM of an invading organism

when antibody binds to antigen, produces an antigen-antibody complex