secondary non-specific defences

• antigens

  secondary defences are used to combat pathogens that have entered the body

  • when a pathogen invades the body, it is recognised as foreign by chemical markers on its outer membrane (called antigens) → protein or glycoproteins intrinsic to plasma membrane our own cells have antigens but since they are recognised the body doesn’t produce a response
• Opsonins

  → protein molecules that attach to antigens on surface of as pathogen • a type of antibody; some aren't very specific - so that they can attach to a variety of pathogenic cells

  role of opsonins is to enhance ability of phagocytic cells to bind + engulf pathogen
• Phagocytes

  first line of secondary defence is phagocytosis → specialised cells in blood + tissue fluid engulfs + digest pathogens
• Neutrophils

  most common phagocytes

  • recognised by multi- lobed nucleus
  • manufactured in bone marrow o travel in blood + often squeeze our of blood into tissue fluid
  • short-lived, but they will be released in large numbers as a result in infection

  → die soon after digesting a few pathogens

  → Dead neutrophils may collect in an area of infection to form a pus
• Macrophages

  larger cells manufactured in bone marrow

  • they travel in blood as monocytes before settling in body tissue
  • many are found in the lymph nodes when they mature into macrophages

  Dendritic cells - type of macrophage - are found in me more peripheral tissues

  • Macrophages play an important role in initiating the specific responses to invading pathogens

  when a macrophage engulps a pathogen, it doesn't fully digest

  → the antigen from suface of pathogen is saved + moved to a special protein complex on surface of cell
• • cell becomes an antigen- presenting cell

  → exposes the antigen on surface so other cells of immune system can recognise antigen

  the special protein complex ensure that the antigen-presenting cell is not mistaken for a foreign cell and attacked by other phagocytes
• Antigen presentation

  antigen - presenting cell moves around the body where it can come into contact with specific cells that can activate the full immune response

  → these are the T- lymphocytes + B- lymphocytes

  • there may only be one T cell + one B cell with the correct recognition site for the antigen

  → therefore the antigen-presenting cells is to increase the chances that the antigen will come in contact with them
• specific immune response

  activation of the specific B + T cells called clones selection

  • this brings into play a complex series of events that leads to the production of antibodies that combat the specific pathogen + memory cells that will provide long term community the whole series of events is stimulated + coordinated by a number of hormone-like chemicals called cytokines
  • these stimulate the differentiation + activity of macrophages, B cells + T cells
• Investigation

  Looking at blood cells

  wear eye protection

  Blood cells can be viewed in a blood smear

  • a thin layer of blood is spread out on a slide, and is stained to make the white blood cells more visible
  • red blood cells are pink in colour ; note that not all have the perfect bioconcave disc
  • monocytes are the largest white blood cells and usually have a large kidney-shaped nucleus
  • Neutrophils have a multi-lobed nucleus
  • lymphocytes are smaller, and nucleus almost fills the cell