Innate Immunity I Flashcards
Describe neutrophils
- Most abundant phagocytes/first line of defence
- Degranulation, phagocytosis and antigen presentation occur
Describe phagocytosis.
- Attach to microorganisms by cell surface receptors
- Pseudopods extend and fuse - form phagosome - fuse with lysosome - forms phagolysosome
- Lysosomal enzymes break down microbe
- Residual waste exocytosed
Describe eosinophils.
- Produced in response to parasitic infections
- Involved in IgE mediated allergic disorders
- Prevent spread of inflammation by collecting in response to chemotactic factors from mast cells
Describe basophils.
- Release heparin - prevent coagulation
- Bind to IgE antibodies - role in allergic reactions (type 1 hypersensitivity)
Define mast cells.
- Release histamines and produces cytokines
- Involved in tissue repair and wound healing
- Hypersensitivity reactions
- Histamines cause dilation of small blood vessels, increase in vascular permeability
Describe monocytes
- Produced in bone marrow and travel to tissue - mature and become macrophages
- Roles in phagocytosis, antigen presentation and cytokine production
- Survive following phagocytosis for months
Describe macrophages.
- Effector cells of innate immune system
- Develop from monocytes
- Perform antigen presentation/activate memory cells
- Can be fixed/free
Describe natural killer cells.
- Role in adaptive/innate immunity
- Non-phagocytic
- Induce apoptosis, attack cells lacking cell surface receptors
What is the main difference between apoptosis and necrosis?
APOPTOSIS - programmed cell death
NECROSIS - accidental cell death
Describe antigen-presenting cells.
- Innate immune cell - activates adaptive immunity
- Detects phagocytosis and digests pathogen to form antigen fragments
- Presented using MHCs
- EXAMPLES: Dendritic cells/B cells/macrophages
Define dendritic cells
- Main APC - activate T helper and memory cells
- Form in bone marrow, circulate in bloodstream, activated by pathogens and mature at target tissues
- MIgrate to lymph nodes where antigen-specific immune response develops
- EXAMPLES: Langerhans cells in skin
What is the difference between MHC Class I and II? PART 1
- CLASS I - displayed by all nucleated cells, recognised by naive CD8 cells/cytotoxic T cells, foreign antigens are endogenous
What is the difference between MHC Class I and II? PART 2
- CLASS II - displayed by APCs, recognised by T helper cells/naive CD4 cells/foreign antigens are exogenous
Describe immature dendritic cells
- Phagocytose pathogens, degrade proteins into small pieces
- Once antigen encountered, activated into mature cells and migrates to lymph nodes
- Upon maturation, present antigen fragments on cell surface using MHC Class II
Outline how immature dendritic cells mature. PART 1
- Senses pathogen/inflammatory signals
- Phagocytose microbe
- Upregulate expression of CD80/CD86 receptors involved in T cell activation
Outline how immature dendritic cells mature. PART 2
- Upregulate CCR7 - chemokine receptor - allows mature dendritic cell to travel through bloodstream to lymph nodes in response to chemokines
- Decreased phagocytic capability
- Greater expression of MHC II - release cytokines/chemokines
How can dendritic cells be involved in disease?
HIV
- Bind to dendritic cells via receptors
- Travel to lymph nodes
- Transferred to CD4+ T helper cells
What are Toll-like receptors?
- Dendritic cells identify pathogens by recgonising PAMPs using pathogen-recognition receptors (PRRs)
- EXAMPLE OF PRRs: Toll-like receptors - link PAMPs to transcription factor activation
Give some examples of inflammatory mediators.
- Cytokines
- Chemokines
- Lipid mediators e.g prostaglandins
Describe cytokines.
- Proteins secreted by immune cells e.g neutrophils, macrophages, NK cells
- Affects behaviour of other cells
- Involved in innate/acquired immunity
Describe interferons.
- Cytokines produced in response to viral infection
- Cause anti viral state in target cells
- Shuts down protein synthesis machinery, preventing viral replication
Outline the role of interleukins
- Inflammation
- Immune cell proliferation and activation
- Increase antibody production
Outline the steps in phagocyte mobilisation. PART 1
- LEUKOCYTOSIS - neutrophil release in response to inducing factors
- MARGINATION - endothelial cells of capillaries in inflamed area project CAM - attach to neutrophils - roll across vessel wall
Outline the steps in phagocyte mobilisation. PART 2
- DIAPEDESIS - movement of neutrophils into interstitial spaces by flattening and squeezing between endothelial cells
- CHEMOTAXIS of neutrophils towards area of injury
- Monocytes arrive - form macrophages
