Immune system and innate immunity Flashcards
The 2 types of immunity
Innate-common set of responses activated by most microbes
Adaptive-individual response to specific antigen exposure. Can change during response through adaptation
Components of innate system:
Physical
Epithelial surfaces (eg skin, GI tract etc) can secrete antimicrobial substances such as defensins
Cytokines such as IL-1 and TNFalpha can increase such secretions
Epithelia also have lymphocytes and mast cells that can create antibodies against LPS (lipopolysaccharide)
Components of innate system:
Cellular-Neutrophils
Medium sized and has a large multilobed nucleus with many organelles
Main functions include phagocytosis, producing antimicrobial peptides and reactive nitrogen and oxygen species
Components of innate system:
Cellular- Macrophages
Large and has a large rounded nucleus with many organelles
Many functions including: Phagocytosis, antigen presentation, complement proteins, cytokines, inflammatory mediators and N/O reactive species.
Components of innate system:
Cellular- Dendritic cells
Large cells with a small nucleus:cytoplasm ratio and has membrane protusion
functions include: antigen inflammatory, interferon, cytokines, co simulatory signals and reactive O species
Structures on microbes not present on mammalian cells
Mannose receptors
Opsonin receptors
Toll like receptors
7TM alpha helical receptors
What happens when innate cells bind to pathogens?
Phagocytosis by macrohages or neutrophils
Killing of infected cells by NK cells
Presentation to t-cells by APC (dendritic) cells
Toll like receptors
Similar to drosophila toll receptors-has 10 mammalian forms
Found in most cells of innate immune system and respond to many microbial markers eg. LPS, ds RNA, and bacterial peptidoglycans
Increased expression of inflammatory genes: TNFalpha, IL-1, IL-12, E-selectin, iNOS
Lipopolysaccharide (LPS)
Endotoxin produced by gram negative cell walls that stimulate the immune system and induces local and systemic inflammation
Potent activator of macrophages inducing cytokine and reactive O species release
Systemic inflammatory response syndrome (SIRS): Fever, neutrophilia, septic shock
Phagocytosis
Done by neutrophils and macrophages though neutrophils are more common
Microbes taken in through endocytosis and fused with lysosome with degrading enzymes (lysozyme, elastase and collagenase)
Reactive O species: super oxide, H202, NO
Stages of phagocytosis
- Bacteria attach to pseudopodia
- Bacterium ingested forming phagosome
- Phagosome fuses with lysosome
- Enzymes digest captured material
- Digestion products released from cell
Complement system
A cascade of plasma protein activated by microbes and has three pathways; lectin, classical and alternative
All of these result in cleavage of C3 into C3A and C3B
This leads to opsonisation and phagocytosis
Zymogens gain activity by cleavage
Cytokines
Mediate many effector functions of the innate system
2 major groups:
TNF/ IL-1- Mostly produced by LPS challenged macrophages and are proinflammatory
stims neutrophil migration to the site
IL-12- produced by macrophages/dendritic cells and promotes NK cytolysis as well as stiming IFN production in t cells and NK cells. IFN stimulates macrophage killing of microbes
Overall innate system
Same response for every pathogen
The cells involved are effector cells that aid in the removal of the pathogen
Cells are recruited to site of action by inflammatory mediators
Types of hypersensitivity
type 1- immediate hypersensitivity
type 2-autoanitbodies
type 3-deposition of immune complexes
type 4- t cell mediated tissue injury
types 2-4 are types of autoimmunity
