What is immunity?
Immunity is the host reaction that results in protection from infectious pathogens, but also includes host reactions against cancer (tumour immunity), tissue transplant and self antigens (autoimmunity)
What is innate immunity?
Innate immunity is also called natural or native immunity. It is the first line of defense. It is the intrinsic mechanism that respond immediately and is mediated by cells and molecules that recognize products of microbes and dead cells and induce rapid protective host reaction.
What is adaptive immunity?
Adaptive immnity is also called acquired or specific immunity. It consists of mechanism stimulated by exposure to microbe and other foreign substances. It develops more slowly than innate immunity, but is even more powerful in combating ifnection.
What are the components of the innate immunity?
- Epithelial cells (Barrier to microbes and produce antimicrobial molecules - defensin) and contains lymphocytes
- Monocytes and neutrophils - Phagocytic cells
- Dendritic cells - Sentinel cells that detect danger and initiate innate immune response
- Innate lymphoid cells (ILC) - lack antigen receptors; instead activated by cytokines and other mediators - produce inflammatory cytokines during early phase of immune reaction.
-Natural killer cells (Type of ILC) - provides protection against viruses and intracellular bacteria - Other cells: eg. Mast cells (inflammatory mediators), epithelial and endothelial cells
- Plasma proteins: Complement system (Alternative and lectin - innate; classic - adaptive), mannose-binding lectin and c-reactive proteins. Surfactant against inhaled microbes
How is the complement system activated?
The complement system is activated by three main pathways:
1. Classic pathway - Antibody-Antigen complex
2. Alternative pathway - Microbial surface molecules (endotoxins, lipopolysaccharides, complex polysaccharides, cobra venom and other substances in the absence of antibody)
3. Lectin payhway - plasma mannose-binding lectin binds to carbohydrates on microbes and directly activate C1
What are the functions of the complement system?
Function: The complement systems are the COPs
1. Inflammation: C5a, C3a and lesser extent C4a - stimulate histamine release from mast cells -> Increase vascular permeability and vasodilation.
C5a is also a chemotactic agent for neutrophils, monocytes, eosinophils and basophils.
C5a actives Lipoxygenase pathway of AA metabolism in neutrohpils and monocytes -> further release of inflammatory mediators.
- Opsonization and phagocytosis: inactive C3b (iC3b) acts as an opsonin on microbial cell walls and promote phagocytosis.
- Cell lysis: deposition of membrane attack complex on cells make them permeable to water and ions and results in osmotic lysis of the cells.
Particularly important for Nesseria bacteria
