Immunity Flashcards
What is a pathogen?
Any microorganism that can cause disease
Bacteria
Prokaryotic cells which can reproduce rapidly by binary fission so a genetic mutation in bacteria can spread quickly and develop resistance.
produce toxins which damage the body
Viruses
-Cannot survive or reproduce outside a host cell
-To reproduce they enter a host cells via complementary receptors
-Kill cells by inhibiting them or causing them to burst
Fungi
-eukaryotic cells that may be singular/multicellular
-obtain food via secreting enzymes to dissolve substrate then absorb the nutrients
-reproduce by producing spores
-pathogenicity depends on level of penetration
Types of infection
Superficial - usually treatable
Sub-cutaneous - treat with antimicrobials
Systematic - usually fatal
How does the body recognise its own cells?
Recognises the specific self-antigens surrounded on the cell surface membrane
How do we not produce an immune response to our own cells?
In the fetus:
1)lymphocytes constantly collide
2) infection is rare due to sheilding
3) lymphocytes will collide with self-antigens
4) If lymphocytes has receptors that exactly fit the self-antigen then they will die
5) the only remaining lymphocytes are those of which fit to foreign antigens
In bone marrow:
1) Lymphocytes will only initially encounter self-antigens
2) Any lymphocytes that initiate immune response to a self-antigen under apoptosis then differentiate into mature cells
3) No anti-self lymphocytes
What is phagocytes?
A type of white blood cell which are produced in the bone marrow before being released into the blood. They are responsible for removing dead cells.
2 main types:
1)Neutrophils
2)Macrophages
Steps for phagocytosis in Neutrophils
1) Chemical products of pathogens act as attractions
2) Phagocytes move towards pathogen
3) Phagocyte has receptors on membrane that recognise and attach to antigen on the surface of the pathogen.
4) Engulf the pathogen to form a phagosome
5) lysosomes move towards vesicle and fuse with it
6) enzymes called lysosomes destroy ingested bacteria by hydrolysis of their cell wall
7) Soluble products from pathogen breakdown are absorbed into cytoplasm of phagocyte
Steps of phagocytosis in macrophages
Capable of moving into organs as well as blood
-carry out phagocytosis but do not fully destroy pathogens
-cut pathogen and display their antigens on their surface which makes the cell antigen presenting which can then be recognised via lysosomes.
Antigen presenting cell
1)Phagocytes which have undergone phagocytosis present pathogens antigens
2)Body cells invaded by virus present some on cell surface
3)Transplanted cells from individuals of same species
4)cancer cells
4 types on t-cells
T-helper cells - CD4 receptor which is a specific shape for 1 antigen only
T-effector cells - cells that are produced after t-helper cells have divided they have the same function of t-helper cells
Cytotoxic t-cells- cells will kill infected and nonself cells
memory t-cell- produced when helper t-cells clone and stay in the body to help mount a quicker response of reinfection
t lymphocytes
Only respond to APC and each cell has a receptor of which is specific to a single antigen
Cell mediated response
1)Pathogen invades the body and antigens are presented on cell surface membrane of a phagocyte
2)Specific receptors on the t-helper cells respond to APC by binding specifically to its antigen
3)Cell is now activated and divides rapidly via mitosis
These cloned cells can develop into:
memory cells
stimulate phagocytes
stimulate b-cells to divide and make antibodies
activate cytotoxic t-cells
What do cytotoxic t-cells do?
-They divide via mitosis and kill infected/non-self cells
-Produce proteins called perforin which makes holes in the cell membrane of pathogens so they become permeable and cell dies
-They are most effective against viruses as it prevents them from multiplying
Other than binding to APC what do t-helper cells do?
-Secrete cytokines a group of hormones that are activated by t-cells or macrophages
-Include growth factors that initiate cell division.
-Cell toxins to speed destruction
-Interferons to protect cells from further infections
-help activate b cells in humoral response
b-lymphocytes
-remain in the bone marrow until matured
-concentrated in lymphnodes and spleen
-each type of b-cell can only make 1 type of antibody and each antibody is specific to one antigen
Humoral Response (primary response)
Clonal Selection
1)Pathogen enters the body with unique antigen
2)the b-cell with complementary antibody attaches
3)antigen enters cell via endocytosis
4)antigen is then processed and presented on the cell surface membrane
5) the t-helper cell with complementary receptor binds to processed antigens and stimulates the b-cell to divide (clonal expansion)
cloned plasma cells then produce and secrete antibodies for the pathogen which then destroy the pathogen. Some may become memory cells.
Humoral Response (secondary)
Plasma cells only survive a few days so memory cells do secondary response:
-if same antigen is encountered again, memory cells will divide rapidly and differentiate into plasma cells which will produce antibodies to kill the cells
-new memory cells will also be made in clonal expansion and will provide long term immunity
-so therefore antibodies are made at much faster rates and concentrations that pathogens are killed before any harm is caused
Describe the structure of an antibody
-Consists of 4 polypeptide chains 2 light and 2 heavy
-They are joined via dulsulfide bridges
-antibodies variable region includes the specific binding site which is unique for a specific antigen (the sequence of amino acids forming the 3D shape determines this)
-hinge region gives flexibility so binding sites can be placed at different angles.
What is agglutination?
-due to binging to 2 antigens at a time they can cause the groups of pathogens to clump together .
The clumps make the pathogens less spread throughout the body so phagocytes can more easily locate them and kill them.
The clumps act as markers that stimulate phagocytes to engulf pathogens they are attached too as they are more likely to collide
What is a monoclonal antibody?
an artificially produced antibody that bind to a specific antigen that activates an immune response
How are monoclonal antibodies produced?
1) a mouse is vaccinated with the pathogen to begin the production of the antibodies
2) Spleen cells that form antibodies are collected
3) fused with myeloma cells
4) forms a hydridoma
5) grown in a lab an antibodies collected
Risks of monoclonal antibodies
-deaths whilst trying to treat patients with multiple sclerosis
-clinical trails where severe organ failure occurred
