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Autoimmunity - an Introduction

Innate and Acquired Immunity

Our immune system uses two different strategies to fight against unwanted invaders: the non-specific innate immune defence and the highly specific adaptive or acquired immune system. Acquired immunity is the basis for our immune memory.

Innate immunity

A macrophage
Flickr ; Urheber: magnaram

Macrophage from mice with two pseudopodia.

The innate immune system comprises the cells and mechanisms that defend the host from infection by other organisms in a non-specific manner. The cells of the innate immune system recognize and respond to pathogens in a generic way, without prior contact to the pathogen. Specialized immune cells like macrophages, natural killer cells or neutrophil granulocytes distinguish foreign microorganisms from the body’s own tissue, incorporate and digest the pathogenic invaders by a mechanism called phagocytosis.

The complement system is another component of innate immunity. More than 30 proteins, most of them soluble in the blood plasma, are activated by a cascade of sequential reactions that leads to the formation of a membrane attack complex. This protein complex inserts into the phospholipid bilayer of the pathogen, disrupts the cell membrane and destroys the intruder.

Activation of the complement system during an immune response
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