4- Barriers to innate immunity

• Cytokines

  Small soluble polypeptides that pass signals
• Hematopoietic stem cells (HSCs)


  • Play role in both immune systems and hematopoiesis
  • Examples: Interleukins, interferons, TNF
• Chemokines


  Type of cytokine
• Chemokines

  • Send 'come here' message necessary to recruit cells to their correct places
  • Bind chemokine receptors (usually G-protein coupled receptors)
• Chemokines are part of the first part of the immune response (happens before even seeing a pathogen)
• Hematopoietic stem cells (HSCs)

  • Found in bone marrow
  • Can self-replicate/ regenerate
  • Pluripotent: can become many different kinds of cells
  • Will lay dormant until necessary
• Hematopoiesis


  Highly regulated process to make all the blood cell types
• Hematopoiesis development

  • Needs the right microenvironments
  • Cytokines: for homing and development (stromal cells)
  • CSF: distinct cytokines-required at specific stages and can determine cell lineage
• Hematopoiesis development


  1. C-kit ligand binds to c-kit receptor

  2. Allows stem cells to respond to other CSFs
• See diagram!
• Physical barriers of innate immunity

  • Skin: Epidermis (many layers, tightly packed epithelial cells, Keratinocytes, Langerhans (dendritic))
  • Dermis: connective tissue, macrophage, dendrites, mast cells
  • Sebum: oily/waxy barrier on skin with some antimicrobial properties
• Pathogens need to overcome the physical barrier to be effective
• Ways pathogens can overcome physical barriers

  • Open wounds
  • Pathogen evolution
  • Secretions that digest skin
  • Vector (like mosquito bite)
• Mucosal tissue


  • Things like lungs, intestines; huge amount of surface area and only one layer of epithelium so very easy to get
  • Permeable barrier: allows for gas exchange but in this case- BAD
• Infections of mucosal tissue


  • C.diff
• Treatment for C.diff

  1. Vancomycin (4/day, 14 days)

  2. Bowel lavage

  3. Fecal transplant
• C.diff is common to reoccur because spores in gut, antibiotics get less effective
• Long term use of antibiotics allows for the C.diff infection