Cell Recognition & The Immune System

how do bacteria damage body cells

produce toxins

how do viruses damage body cells

use host cells to replicate before bursting out and destroying cells

how do protists damage body cells

take over cells and break them open

how do fungi damage body cells

digest living cells to destroy them and produce some toxins

what are the differences between specific and non specific defence systems

non-specific are quick and respond in the same way for all pathogens - eg. physical barriers

specific are slower but produce a specific response for each pathogen - eg. cellular response

what are antigens

unique molecules (usually proteins) found on the surface of cells

these allow the immune system to be able to distinguish between body cells and foreign cells

what are 4 cells and molecules that the immune system can recognise with antigens

pathogens

abnormal body cells (cancer)

toxins

cells from other organisms (eg. an organ transplant)

is phagocytosis specific or non-specific

non-specific

describe the process of phagocytosis

the pathogen releases a chemical that attracts a phagocyte

the phagocyte recognises the pathogens antigens as non-self, this causes the phagocyte to bind to the pathogen

the phagocyte engulfs the pathogen, it is now contained within a vesicle called a phagosome

the lysosome, which contains hydrolytic enzymes known has lysozymes, fuses with the phagosome - forming a phagolysosome

lysozymes digest and destroy the pathogen

the phagocyte presents the pathogen’s antigens on its surface to activate other cells in the immune system, the phagocyte is now referred to as an antigen presenting cell (APC)

what are T cells

lymphocytes that mature in the thymus

they are involved in cellular response, where they respond to antigens presented on body cells

what are B cells

lymphocytes that mature in the bone marrow

they are involved in humoral response where they produce antibodies found in body fluids

what do helper T cells (T_H ) do

they have receptors on their cell surface that bind to complimentary antigens on antigen presenting cells

after binding they can form memory cells, stimulate B cells or phagocytes and activate cytotoxic T cells (T_c)

what do cytotoxic T cells (T_c) do

the kill abnormal and foreign cells by producing a protein known as perforin

this protein makes a hole in the cell surface membrane, causing it to become freely permeable and leading to cell death

what are memory T cells

cells which provide long term immunity against specific pathogens

they provide a rapid response if the body is infected by the same pathogen

what are the stages of cellular response

phagocytes engulf pathogens and display their antigens on the cell surface, they are now known as antigen-presenting cells

helper T cells with complementary receptors binds to these antigens

on binding, the helper T cell is activated to divide by mitosis to form identical clones

what can clones T cells do

develop into memory cells - giving long term immunity

stimulate phagocytosis

stimulate division of B cells which produce antibodies

activates cytotoxic T cells, which kill infected cells

what is humoral response

production of specific antibodies to destroy pathogens

how are B cells involved with humoral response

B cells have antibodies on their cell surface membrane that bind to complementary antigens

on doing so, they engulf the antigens and display them on their cell-surface to being APCs

once activated, B cells can divide into plasma and memory cells

how are plasma cells involved in humoral response

these are types of B cells which produce and secrete antibodies against a specific antigen

they only live a few days

how are memory cells involved in humoral response

these are types of B cells that provide long-term immunity against specific pathogens

they have a much longer lifespan than plasma cells

they rapidly divide into plasma cells if the body is re-infected by the same pathogen

how are helper T cells involved in humoral response

they bind to APCs to activate the division of B cells

what are the stages of humoral response

a B cell with a complementary antibody binds to the antigens on a pathogen

the B cell engulfs the pathogen and presents its antigens on the cell-surface to become an APC

clonal selection - activated T_H cells bind to the B cell, causing activation of the B cell

clonal expansion - the activated B cell divides by mitosis to form plasma and memory cell clones

the clones plasma cells produce and secrete the specific antibody which is complimentary to the antigen on the pathogen’s surface, these antibodies attach to antigens on pathogens and destroy them

the memory cells circulate the blood and tissue fluid, ready to divide if the same pathogen is detected

what is clonal selection

the B cell with the correct antibody is selected for cloning by being activated by a helper T cell

what is clonal expansion

the division of specific B cells to produce genetically identical clones

what are the differences between primary and secondary immune response for:

symptoms

cells activated

number of antibodies produced

what is the structure of antibodies

Y-shaped glycoproteins

4 polypeptide chains - 2 light and 2 heavy

the polypeptide chains are held together via disulphide bridges

what are the 2 regions on antibodies

constant region - the same for all antibodies and binds to receptors on cells such as B cells

variable region - this is different for each antibody as its shape is complimentary to a specific antigen, this region binds to antigens

what 3 ways do antibodies help destroy pathogens

agglutination - clumping allows easier phagocytosis

neutralisation of toxins - antibodies bind to toxins, inactivating them

prevent pathogens from binding and infecting body cells

how do antibodies prevent pathogens from binding to body cells

when antibodies bind to a pathogen’s antigens, they block cell-surface receptors needed to bind to host cells

this means that the pathogen cannot bind to or invade host cells