Week 31 - The immune response part 1 and 2

• Immunology was discovered first

  430 BC
• Microbes we fight every day

  • Bacteria
  • Fungi
  • Viruses
  • Parasites
• Immune system

  • Antibodies circulating in our blood stream
  • Immune cells in our blood and in areas rich in white cells such as the bone marrow, thymus, spleen, and lymph nodes
• Immune response shift to red alert

  Starts with an acute inflammatory response starting at the site of infection
• Exterior Defences

  • Skin
  • Mucous membranes
  • Secretions
  • Commensal organisms
• Cells of the Immune System

  • Consist of white cells (leukocytes) and specialised areas called lymphoid tissues (lymph nodes)
  • Lymphocytes circulate within both the lymph vessels and the blood vessels and are part of the adaptive immune response
  • Non-lymphocytes (granulocytes, macrophages, and neutrophils) are cells of the innate immune system
• The production of all the cell types found in the immune system starts from a self-renewing bone marrow stem cell
• Macrophages are important phagocytic cells, taking up bacteria and small parasites, and also present antigen to T cells of the adaptive immune response
• Dendritic cells are the most important antigen-presenting cells of the body, as they can activate resting T cells which have never seen antigen
• Neutrophils are the most abundant white cell in the blood and are phagocytic, effective in fighting bacterial infections
• Eosinophils are involved in causing damage to parasitic worms and have a role in asthma during an allergic response
• Basophils help to produce an inflammatory response within the surrounding tissues during an allergic reaction or attack by parasites
• Mast cells can release granules during an inflammatory or allergic response that contain histamine and other active agents, fighting infections caused by a range of parasitic worms
• Natural killer cells (NK cells) can kill intracellular infections by bacteria and viruses by destroying the infected cell, and can also target and kill tumour cells in the body
• Phils fight infections caused by a range of parasitic worms
• Natural killer cells (NK cells)

  • They are large granular lymphoid-like cells which can kill intracellular infections by bacteria and viruses by destroying the infected cell the pathogen is in at the time
  • They can also target and kill tumour cells in the body
  • They lack foreign antigen-specific receptors and are part of our innate immune system
• T and B lymphocytes (lymphoid lineage)

  • Both T and B cells are part of the adaptive immune system
  • T and B cells are only seen in vertebrate species
• Innate and adaptive immunity


  Must work together to destroy microorganisms
• The distribution of lymphoid tissues in the body
• Lymph nodes are part of the lymphatic circulation and are full of leukocytes which capture pathogens that have entered the local tissues or blood
• Lymph nodes are part of the “encapsulated” secondary lymphoid tissues of the body, such as the spleen
• “Lymph” is extracellular fluid filtered from the blood present in the tissues and is continuously returned to the blood via lymphatic vessels
• Circulating lymphocytes meet antigen in lymph nodes local to the infected site
• Lymphocytes that have never seen antigen (naïve lymphocytes) recirculate constantly between the lymph nodes of the body
• If they encounter a pathogen within the draining lymph node they become activated and return to the bloodstream to find the infected tissue to destroy the infectious agent
• This whole process takes 4-6 days! Luckily the innate immune response is already tackling the infection from day 1
• Humans are very polymorphic in their MHC molecules expressed on all body cells of the body (except erythrocytes)
• Of all human genes sequenced, the MHC is the most polymorphic of all
• Genetic information about MHC status is relayed by androgen-based pheromones in mammals
• Numerous studies in rodents have now established that MHC genotype is involved in odour production, and such odours are used in individual discrimination
• House mice learn the MHC identity of their family during development and avoid mating with individuals carrying familial MHC genes; they do so through the use of odour cues from urine
• Inflammation


  The four Latin words traditionally defining inflammation: calor = heat, dolor = pain, rubor = redness, tumor = swelling
• The effects of inflammation are due to the activity of local cytokines made by white blood cells in the infected tissue
• Cytokines produced by macrophages and neutrophils

  Elevate body temperature to help the body fight infectious organisms
• Endogenous pyrogens, such as TNF-α, cause fever by inducing the production of prostaglandin E2
• Prostaglandin E2 acts on the hypothalamus in the brain


  Resulting in increased production of heat from the brown fat of the body and increased vasoconstriction
• Bacteria grow better at lower body temperatures, whereas the adaptive immune response is more intense at higher body temperatures
• Mild fever promotes phagocytosis
• Phagocytosis

  Phagocytes arrive at a site of inflammation by chemotaxis, infectious agent is taken into a phagosome, lysosomes fuse with the phagosome to form a phagolysosome, pathogen is killed due to enzymes in the lysosome, some components are expelled while others are displayed on the cell surface on an MHC molecule
• White cells, like neutrophils, migrate into tissues and perform phagocytosis through extravasation