Cell recognition

• What is the process of direct ELISA testing?

  • antigens from patient sample are bound to the inside of the well
  • a detection antibody (with an attached enzyme) that is complementary to the antigen is added
  • if antigen is present it will be immobilised on the inside surface of the well and the detection antibody will bind to it
  • the well is washed to remove any unbound antibodies
  • a substrate solution is added
  • if detection antibody is present, the enzyme reacts with the substrate to give a colour change
• What is the process of indirect ELISA testing?

  • antigens are bound to the base of the well
  • sample of patient blood plasma is added, antibodies bind to antigens if complementary
  • wash out well to remove unbound antibodies
  • add more antibodies that have an enzyme attached, which bind to 1st antibodies
  • wash out well again to remove 2nd antibodies
  • add substrate solution, if binds with enzyme there is a colour change
• Pathogen


  a microorganism that causes disease
• antigen


  a protein found of the surface of a cell, which causes the body to make an immune response against it
• lymphocytes 


  a type of immune cell that is made in the bone marrow and found in the blood
• phagocytes


  type of immune cell that can surround and kill microorganisms
• What is a non-specific response?


  response in immediate and the same for all pathogens
• What is a specific response?


  response is slower and specific to each pathogen
• two examples of a non-specific response


  • physical barrier e.g. skin
  • phagocytosis
• two examples of a specific response

  • cell mediated response e.g. T lymphocytes
  • humoral response e.g. B lymphocytes
• T cells


  • mature in the thymus gland
  • immunity involving cells
• B cells


  • mature in the bone marrow
  • humoral immunity
• helper T cell


  produce a chemical signal, which causes proliferation of specific cytotoxin T cells and effector B cells

  • activate B cells
  • produce memory cells
• cytotoxic T cells


  recognise infected cells or tumours and destroy them by secreting perforin that rupture their membranes
• memory cells


  circulate in the blood after the pathogen has been removed

  • divide and rapidly produce a secondary immune response
• effector B cells


  multiply and give rise to plasma cells when activated by helper T cells

  • some will become B cells
• plasma cells


  develops from effector B cells and produces antibodies
• T cells can act on the following cells:


  • phagocytes that present an antigen
  • infected body cells present an antigen
  • recognise transplanted cells with different antigens
  • cancer cells present antigens
• T cell clones 


  • stimulate B cells
  • stimulate phagocytes
  • activate cytotoxic T cells
  • develop into memory cells
• What is the cell mediated response?


  • phagocyte presents pathogens antigen on cell surface
  • T helper cell binds to complementary shape
  • T helper cell divides by mitosis and clonal expansion
  • some become memory cells incase of reinfection
  • T helper cells release cytokines, which activates cytotoxic T cells
  • these release parforin, which breaks down the cell membranes and causes cell lysis/death
• Phagocytosis


  • phagocyte detects chemicals released by a foreign intruder
  • the phagocyte adheres to the foreign cell and engulfs it in a vacuole by an infolding of the membrane
  • lysosomes fuse with the vacuole and release their contents into it
  • the bacterium id digested by the enzymes and the breakdown products are absorbed by the phagocyte
• antigen


  protein or glycoprotein that stimulates an immune response
• plasma cells


  • primary immune response
  • secrete antibodies directly
  • survive only two days
  • response is slow and person will get ill
• memory cells


  • secondary immune response
  • in blood and tissue fluid
  • divide rapidly when encounter antigen
  • rapid response and person won't get ill
• antibodies


  • known as immunoglobulins
  • globular glycoproteins
  • heavy and light chains are polypeptides
  • held together by disulphide bridge
  • order of amino acids determines the shape of bonding site
• antibody uses:


  • some act as labels to identify antigens for phagocytosis
  • some work as antitoxins - block toxins
  • some attach to bacterial flagella making them less active and easier for phagocytosis to engulf
  • some cause clumping together of bacteria making them less likely to spread
• monoclonal antibodies


  antibodies with the same tertiary structure and produced from B cells
• polyclonal

  variety of different antibodies
• How are monoclonals antibodies produced?


  • mouse is injected with a specific pathogen and its immune system responds
  • specific B lymphocytes produce antibodies
  • tumour cells rapidly divide by can't make antibodies
  • the B cells are combined with tumour cells
  • hybridoma cells can make specific antibodies. They are screened to make sure they are producing the right one
  • hybridoma cells copy themselves and produce antibodies
  • these are called monoclonal antibodies
• Active immunity


  • takes time for enough B and T cells to be produced to mount an effective response
  • artificial active immunity is acquired by vaccination
  • natural active immunity is acquried due to infection
• Passive immunity 


  • B and T cells are not activated
  • antigens don't have to be encountered to make antibodies
  • appear immediately but protection is temporary
  • artificial passive immunity: can be injected with antibodies from a donor -> short term protection
  • natural passive immunity: breast milk -> mothers antibodies pass across placenta to foetus
• herd vaccination


  when all or almost all of the population are given the vaccination
• What are the difficulties with vaccinations?


  • side effects
  • migration
  • not enough of the population is vaccinated
  • may only be effective for a few years
  • pathogen may mutate
• Two types of antigenic variation 


  • antigenic drift: small changes but can still be recognised by memory cells
  • antigenic shift: large changes and cannot be recognised by memory cells
• How do vaccinations work?

  • dead/inactive/attenuated pathogen injected
  • helper T cells recognise antigens on pathogen
  • T helper cells activate B cells
  • plasma cells produce antibodies
• How is HIV transmitted?

  Infected body fluid AND entry to the body
• What ways is HIV transmitted?


  • unprotected sexual intercourse
  • injected drug use
  • infected mother to her infant
  • blood transfusion/organ transplant
  • healthcare setting
• How does HIV initially enter the body after infection?

  HIV enters the bloodstream and circulates
• What protein does HIV bind to on T helper cells?

  HIV binds to the protein called CD4
• What happens when the HIV protein capsid fuses with the cell membrane?

  The RNA and enzymes of HIV enter the helper T cell