Opsonisation, MAC, Cytolysis, Inflammation PDF

Preview

Summary

Principles of Immunology...

Description

Opsonisation - After “Central Event”, C3b molecules are produced , a reactive thioester becomes exposed in C3b which bind to microbial surfaces o Reacts with proteins and carbohydrates o They bind to “unprotected microbial surfaces”, that is why C3b cant bind to our “protected” cell surfaces - Phagocytes have receptors for C3b and will recognise it. C3b is called an “Opsonin” - Opsonins promote phagocytic cell function - Microbial cells that are have opsonins are more readily phagocyted, therefore: o Increases rate of phagocytosis o Increases rate of microbial clearance

MAC-mediated Cytolysis - C5b6789(n) assemble to form the Membrane Attack Complex - Formation of a “fully active C9 ring” is accomplished by binding of 12-18 copies of C9, forming a transmembrane pore, and disrupts of membrane o External face of the pore is hydrophobic which allows to interact with membrane o Internal face of the pore is hydrophilic which allows free diffusion of water and other molecules in and out of microbe o Many pores formed will make it impossible for the microbe to survive which results in uncontrolled of influx of ions and water, osmotic lysis - Because MAC associates with phospholipid bilayer, it is more effective with gram-negative bacteria, nucleated cells, and enveloped viruses

Inflammation - Action on Mast Cells and Basophils o Complement components involved: C5a, C3a, C4a (anaphylatoxins) o C5a about 20 times more potent than C3a, and 2500 times more potent than C4a o They are anaphylatoxins (or pro-inflammatory mediators) because they activate other cells o These anaphylatoxins produce localised inflammatory responses via degranulation of mast cells and basophils  Degranulation – is the release of substances of those cells  These substances are more inflammatory mediators, like Histamine, (or prostaglandins, etc)  Histamines causes enhanced blood vessels permeability to other plasma components and leukocytes to the site of infection...