immunity - innate and adaptive

• only a small percentage of microbes are pathogenic, however those that are pathogenic are good at invading our tissues when getting past certain barriers
• our immune system has the ability to fight:

  • viruses
  • bacteria
  • protozoans (e.g- malaria, amoebas)
  • fungi
  • parasitic animals (e.g- tapeworms, flukes)
• What are the two types of immune system?

  innate and adaptive
• innate immune system

  • components found throughout all the animal and plant kingdom
  • non-specific
  • no memory
• adaptive immune system:

  • found only in vertebrae animals
  • highly specific
  • has memory - gives us the ability to recover from an infection and then have protection when exposed to the same pathogen
• (innate) physical and chemical skin barriers:

  • skin
  • normal flora found on the skin
  • mucus and cilia in respiratory tract
  • low pH of stomach
  • antimicrobial peptides
• Pathogen recognition:

  • microbes have different cell surface markers (antigens) than our cells
  • cells will recognise these pathogens associated molecular patterns (PAMPs), basically pathogen antigens, and phagocytise
  • markers are not specific - found on a wide range of microbes
• types of white blood cells involved in the immune system:

  • mast cells
  • macrophages
  • natural killer cells
  • dendritic cells
  • monocytes
  • neutrophils
  • basophils
  • eosinophil
• mast cells:

  • location = connective tissues, mucus membranes
  • induces inflammation and dilates blood vessels
  • involved in wound healing and defense against pathogens
  • may also be responsible for allergic reactions
• macrophages:

  • location = migrates from blood vessels to tissues
  • phagocytic cell that consumes foreign pathogens and cancer cells
  • stimulates response of other immune cells
• natural killer cells:

  • location = circulates blood and migrates into tissues
  • kills tumour cells and virus-infected cells
• dendritic cells:

  • location = present in epithelial tissue e.g skin, lung tissues, digestive tract
  • migrates to lymph nodes upon activation
  • presents antigens on its surface, thereby triggering adaptive immunity
• monocytes:

  • location = stored in spleen, moves through blood vessels to infected tissues
  • differentiates into macrophages and dendritic cells in response to inflammation
• neutrophils: (involved in phagocytosis)

  • location = migrates from blood vessels into tissues
  • first responders at site of infection/trauma
  • abundant phagocytic cell represents 50-60% of leukocytes
  • releases toxins that kill/inhibit bacteria and fungi
  • recruits other immune cells to site of infection
• basophils:

  • location = circulates blood and migrates into tissues
  • responsible for defense against parasites
  • releases histamines that cause inflammation
  • may be responsible for allergic reactions
• eosinophils:

  • location = circulates blood and migrates into tissues
  • releases toxins that kill bateria and parasites
  • also causes tissue damage
• adaptive immunity:

  • cells = B cells and T cells (lymphocytes)
  • can take days/weeks to become upregulated
  • primary and secondary response = has memory
  • highly specific antibodies made by B cells and T-cell receptors made by T cells
• • innate immune system recognises PAMPs found on wide variety of microbes
  • B cells and T cells distinguish between different motifs (epitopes) found on individual microbe = specificity
• T cells = cell-mediated
• B cells = humoral response
• cell- mediated response = based on Major Histocompatibility complex (MHC) - antigen presenting molecules
• T cells:

  • mature in the thymus
  • produce T cell receptor (TCR) that is membrane bound
  • encoded in our DNA
• three types of T cells:

  • (Th) helper T cells = CD4 markers
  • (Tc) cytotoxic T cells = CD8 markers
  • T regulatory cells
• cell mediated response

  1. an antigen presenting cell (APC) processes antigen to be presented on the MHC to a T cell
  2. helper T cells will then release cytokines and upregulate B cells
  3. other immune cells will go through mitosis to make clones of themselves
  4. cytotoxic T cells will kill infected self cells or altered (tumour) self cells
• example of cell-mediated response:

  • a cell is infected with a virus
  • it will present some of that virus on its MHC class 1
  • the Tc cell will then force that self cell to go through apoptosis
• Humoral response = B cells
• what are the two types of B cells involved in the humoral response?

  plasma cells and memory cells
• where do B cells mature?

  in the bone marrow
• what do plasma cells make?

  antibodies, which are proteins encoded for in our DNA
• each plasma B cell produces antibodies with a specific variable region that recognises a specific epitope - can be secreted or membrane-bound on the B cell
• 5 types of antibodies:

  • IgA
  • IgD
  • IgE
  • IgG
  • IgM
• IgA

  • found in mucus, saliva, tears and breast milk
  • protects against pathogens
• IgD

  • part of the B cell receptor
  • activates basophils and mast cells
• IgE

  • protects against parasitic worms
  • responsible for allergic reactions
• IgG

  • secreted by plasma cells in the blood
  • able to cross the placenta into the fetus
• IgM

  • may be attached to the surface of a B cell or secreted into the blood
  • responsible for early stages of immunity
• function of antibodies:

  • neutralisation
  • opsonisation
  • activation of complement
• neutralisation - prevents binding
• opsonisation - promotes phagocytosis
• activation of complement - the complement system is a secondary accessory system to the immune system