immunity

• cell mediated response - t lymphocytes
• humoral response - b lymphocytes
• non specific:

  • physical barrier
  • phagocytosis
• specific:

  • cell-mediated
  • humoral response
• self recognising:

  • lymphocytes that have receptors complementary to the body’s own cells
  • these lymphocytes die or are suppressed
  • the only remaining lymphocytes are the ones that fit foreign antigens
• phagocytosis:

  • chemical products of pathogens cause the phagocytes to move toward the pathogen
  • phagocytes then attach to the pathogen and surround the pathogen with its membrane
  • phagocytes then engulf the pathogen to form a vesicle, called a phagosome
  • lysosome fuses with the phagosome forming a phagolysosome
  • lysozymes in the phagolysosomes hydrolyse the pathogens
  • waste products that cannot be used for metabolism are taken out of the cell by exocytosis
• b cells - mature in bone marrow and produce antibodies
• t lymphocytes - mature in the thymus glands
• cell mediated response:

  • antigens of pathogens are placed on cell surface membranes of phagocytes or body cells, becoming antigen presenting cells
  • T-helper cells with CD4 receptors complementary to the antigen on the antigen-presenting cells undergo clonal selection
  • attachment activates T-helper cells to divide rapidly by mitosis clonal expansion)
  • cloned T-helper cells develop into memory cells, stimulate B cells to divide, release cytokines to aid phagocytosis, activate cytotoxic T cells
  • cytotoxic t cells release perforin that causes the pathogen to perforate
• humoral response:

  • antigen enters B cell by endocytosis and is presented on its surface
  • T helper cells with complementary CD4 receptors bind to the processed antigen (clonal selection)
  • this stimulates the B cells to rapidly divide by mitosis (clonal expansion)
  • the B cells develop into plasma cells or memory cells
• plasma cells:

  • produce antibodies that are complementary to the antigen
  • antibosidies from antigen-antibody complexes with the antigens and cause pathogens to stick together (agglutination)
  • this makes phagocytosis more efficient, as more pathogens are engulfed and hydrolysed in a given time
• memory B cells:

  • responsible for secondary immune response
  • circulate in blood and tissue fluid
  • when they encounter the same antigen at a later date, they rapidly divide and develop into plasma cells and more memory cells
  • provide long term immunity
  • more antibodies secreted at secondary response
• structure of antibody

  A) antigen-binding sites

  B) light chain

  C) variable region

  D) heavy chain

  E) constant region

  F) receptor binding site

  
• variable region of an antibody is different for each antibody
• antibodies cause agglutination of bacterial cells, making it easier for phagocytes to locate them as they are less spread out within the body.

  they also act as markers that stimulate phagocytes to engulf bacteria cells
• monoclonal antibodies as drugs:

  • monoclonal antibodies are specific to antigens on cancer cells
  • antibodies given to a patient with cancer and the antibodies form antigen- antibody complexes with the cancer cell antigen
  • antibody blocks the signals that stimulate the cancer cells to grow uncontrollably
• ELISA testing (enzymes linaked immunosorbant assay) uses antibodies to test for the presence and quantity of a particular protein.

  it is used to test for HIV and the pathogens of diseases, such as tuberculosis and hepatitis
• elisa testing:

  • apply sample to a surface, to which all the antigens of the sample will attach
  • wash the surface several times to remove any unattached antigens
  • add the antibody that is specific to the antigen that is being detected and leave the two to form antigen-antibody complexes
  • wash the surface to remove excess antibody
  • add a second antibody, with an enzyme attached to it, that binds to the first antibody
  • add colourless substrate of the enzyme, the enzyme acts on the substrate to change it into a coloured product
  • amount of antigen present is relative to intensity of the colour
• ethical uses of monoclonal antibodies

  • production uses mice. deliberately inducing cancer in mice is an ethical issue
  • has been used to successfully treat a number of diseases, but has been some deaths associated to the use of monoclonal antibodies in the treatment of multiple sclerosis
• passive immunity:

  • introduction of antibodies into individuals from an outside source
  • immunity is acquired immediately
  • no long lasting immunity
  • anti-venom given to victims of snake bites
  • immunity acquired by fetus when antibodies pass across the placenta from the mother
• active immunity:

  • stimulating the production of antibodies by the individuals own immune system
  • direct contact with the pathogen or its antigen is necessary
  • long lasting
• natural active immunity:

  • individual infected under normal circumstances.
  • body produces its own antibodies
• artificial active immunity:

  • vaccination
  • inducing an immune response in an individual, without them suffering the symptoms of the disease
• vaccine:

  • introduces one or more types of antigen from the pathogen
  • antigens stimulate an immune response
  • memory cells are produced and remain in blood
  • allow a greater, more immediate response to future infection
  • rapid production of antibodies
  • infection is quickly overcome before harm is caused and with few, if any, symptoms
• successful vaccination program:

  • needs to be economically available to immunise most of the vulnerable
  • needs to have few side effects, if any, from vaccination
  • means of producing, storing and transporting vaccines must be available
  • means of administering the vaccines properly
  • must be possible to vaccinate the vast majority of the population to achieve herd immunity
• herd immunity:

  • achieved when a sufficiently large enough portion of the population is vaccinated to make it difficult for a pathogen to spread within that population
• herd immunity is important because it is never possible to vaccinate the entire population.
• ethics of vaccines:

  • production of vaccines uses animals, animal cruelty
  • vaccines may have side effects that cause long term harm
  • testing vaccines is risky, should people be asked to accept the risk in the interest of public health?
  • is it ethical to trial new vaccines with unknown health risks in countries where the disease is common, because they have the most to gain if the vaccine is successful?
• HIV

  A) attachment protein

  B) capsid

  C) lipid envelope

  D) matrix

  E) reverse transcriptase

  F) genetic material (RNa)

  
• HIV - human immunodeficiency virus

  leads to AIDS (acquired immune deficiency syndrome
• one of the enzymes inside the capsid of HIV is reverse transcriptase, which catalyses the production of DNA from RNA. This ability allows HIV to be classified as a retrovirus
• HIV replication:

  • HIV enter bloodstream + circulates the body
  • attachment protein on HIV binds to the CD4 receptors on T helper cells
  • protein capsid fuses with cell surface membrane, RNA and enzymes of HIV enter T helper cell
  • HIV reverse transc
• HIV replication part 1 :

  • HIV enter bloodstream + circulates the body
  • attachment protein on HIV binds to the CD4 receptors on T helper cells
  • protein capsid fuses with cell surface membrane, RNA and enzymes of HIV enter T helper cell
  • HIV reverse transcriptase converts virus’s RNA into DNA
  • HIV DNA inserted into cell‘s DNA in the nucleus
• HIV replication part 2:

  • HIV DNA makes mRNA to make new viral proteins and RNA to go into a new HIV
  • mRNA undergoes protein synthesis
  • new HIV proteins and RNA move to cell surface membrane and assemble into HIV
  • HIV particle breaks off from the T-helper cell, with a piece of its cell surface membrane which forms the lipid envelope
• antiretroviral drugs are used to treat HIV infection
• antibiotics against bacteria:

  • antibiotics inhibit the enzymes required for synthesis and assembly of peptide cross-linkages in bacterial cell walls
  • this weakens the walls, making them unable to withstand pressure due to water moving into the cells by osmosis, causing the cell to burst
• antibiotics against viruses:

  • antibiotics are ineffective on viruses beaches there are no metabolic mechanisms or cell structures for them to disrupt
  • viruses have a protein coat (capsid) rather than a murein cell wall so they do not have sites where antibiotics can work
  • when the viruses are within the organisms own cells, the antibiotics cannot reach them