Cells and the immune system Flashcards
What molecules generate an immune response when detected by the body?
Antigens
Where do antigens found and how are they used?
-Found on the surface of the cells
-Used by the immune system to identify pathogens, abnormal body cells and toxins
What are the 4 stages of 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
Explain the first stage of the immune response and how it works-
-Phagocytes engulf pathogens
-A phagocyte is a type of white blood cell that carries out phagocytosis (engulfment of pathogens)
-they are found in the blood and in tissues and are the first cells to respond to an immune system trigger inside the body.
How it works-
1)A phagocyte recognises the foreign antigens on a pathogen
2)Cytoplasm of the phagocyte moves around the pathogen, engulfing it
3)Pathogen is now contained in a phagocytic vacuole in the cytoplasm of the phagocyte
4)A lysosome (contains lysozymes) fuses with the phagocytic vacuole, Lysozymes break down the pathogen.
5)The phagocyte then presents the pathogens antigens- sticks the antigens on its surface to activate other immune system cells
Explain the second stage of the immune system
-Phagocytes activate T-cells
-T-cell is another type of white blood cell
-It has receptor proteins on its surface that bind to complementary antigens presented by phagocytes. This activates the T-cell
-Different types of Tcells respond in different ways.
-Helper T-cells release chemical signals that activate and stimulate phagocytes and cytotoxic T-cells, which kill abnormal and foreign cells.
-Helper T-cells also activate the B-cells, which secrete antibodies
Which cells secrete antibodies?
B-cells
Explain the third stage of the immune system and how it happens-
-T-cells activate B-cells, which divide into plasma cells
-B-cells ( B-lymphocytes) are type of white blood cell that are covered with antibodies
-Each B-cell has a different shaped antibody on its membrane, so different ones bind to different shaped antigens
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 called clonal selection
3)The activated B-cell divides into plasma cells
What are antibodies?
Proteins that bind antigens to form an antigen-antibody complex
Explain the forth (last) stage of the immune system-
-Plasma cells make more antibodies to a specific antigen
-Plasma cells are identical to the B-cells. They secrete lots of antibodies specific to the antigen. These are called monoclonal antibodies. They bind to the antigens on the surface of the pathogen to form lots of antigen-antibody complexes.
-An antibody has two binding sites, so can bind to two pathogens at the same time. Means that pathogens become clumped together- called agglutination.
-Phagocytes then bind to the antibodies and phagocytose many pathogens at once- destruction of pathogens carrying the antigen in the body
The specificity of an antibody depends on its ……. which form the antigen binding sites
-Variable regions
What includes the cellular immune response?
-The T-cells and other immune system cells that they interact with (phagocytes) form the cellular response
What includes the humoral immune response?
-B-cells, clonal selection and the production of monoclonal antibodies form the humoral immune system
How does primary immune response work?
-when an antigen enters the body for the first time it activates the immune system- primary response
-Primary response is slow because there arent many B-cells that can make the antibody needed to bind to it.
-Eventually body produces enough of the right antibody to overcome the infection, meanwhile the infected person will show symptoms of the disease
-After being exposed to an antigen, both T-and B-cells produce 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
-Person is now immune- immune system has the ability to respond quickly to a second infection
How does secondary immune system response work?
-If the same pathogen enters the body again, the immune system will produce a quicker, stronger immune response- the secondary response
-Clonal selection happens faster. Memory B-cells are activated and divide into plasma cells that produce the right antibody ti the antigen. Memory T-cells are activated and divide into the correct type of T-cells to kill the cell carrying the antigen
-Gets rid of the pathogen before showing any symptom
How do vaccines work?
-Contain antigens that cause your body to produce memory cells against a particular pathogen without the pathogen causing a disease
-Can become immune without getting any symptoms
What is herd immunity?
-Vaccines protect individuals that have them and because they reduce the occurrence of the disease, those not vaccinated are also less likely to catch the disease
Disadvantage of taking a vaccine orally.
-It could be broken down by enzymes in the gut or the molecules of the vaccine may be too large to be absorbed into the blood
What is antigenic variation
-Different antigens are formed due to changes in the genes of a pathogen
-When you are infected the second time, memory cells produced from the first infection will not recognise the different antigens, so the immune system has to start from the scratch and carry out a primary response against the new antigens
-HIV and influenza virus show antigenic variation
How antigenic variation affects the production of vaccines?
-Influenza vaccine changes every year- antigens on the surface of the influenza virus change regularly, forming new strains of the virus
-Memory cells produced from vaccination with one strain of influenza will not recognise other strains with different antigens. -strains are immunologically distinct
What is active immunity?
-Immune system makes its own antibodies after being stimulated by an antigen
1)Natural- after catching a disease
2)Artificial- after vaccination containing a harmless dose of antigen
What is passive immunity?
-Being given antibodies made by a different organism
1)Natural- baby becomes immune due to the antibodies it receives from its mother through placenta and in breast milk
2)Artificial- being injected antibodies from someone else
Differences of active and passive immunity?
Active-
-requires exposure to antigen
-Takes a while to develop
-Memory cells are produced
-protection is long term because the antibody is produced in response to complementary antigen being present in the body
Passive-
Protection is short term because the antibodies given are broken down
What are monoclonal antibodies?
-Antibodies produced from a single group of genetically identical B-cells (plasma cells)- identical in structure
How does targeting drugs to a particular cell type work- cancer cells
1)Different cells in the body have different surface antigens
2)Cancer cells have antigens called tumour markers that are not found on the normal body cells
3)Monoclonal antibodies can be made that will bind to the tumour markers
4)Can attach anti-cancer drugs to the antibodies
5)When the antibodies come into contact with the cancer cells they will bind to the tumour markers
6)Drug will only accumulate where there are cancer cells
7)So the side effects of an antibody-based drug are lower than other drugs because they accumulate near specific cells
