Immune System: Innate Immunity

•      innate immunity

       

Let's learn about innate immunity. Our bodies have a number of ways to fightoff pathogens. One category of defense is called innate immunityor non-specific defense. In innate immunity the same kind of defenseis used against all types of pathogens.

 Three types of innate immunity are mechanicalbarriers, cells and chemical mediators. Let's take a closer look at mechanical barriers. The keratonized or hardened cells of the skinform a natural barrier against pathogens. The mouth is also a barrier and is lined withmucous containing lysozymes that work to destroy pathogens. The stomach contains hydrochloric acid thatdestroys pathogens. Next we'll look at how cells form a line ofdefense against pathogens.

 Some cells engulf pathogens. This is called phagocytosis. The cell engulfs the pathogen and then enzymeswithin the cell work to destroy it. Inflammation is another form of innate immunity. Signs of inflammation include heat, redness,swelling and pain. During inflammation cells known as mast cellsrelease chemicals that promote inflammation. These include histamine, kinins, prostaglandinsand leukotrienes.

 These substances work to increase capillarypermeability and promote vasodilation. Other cells such as neutrophils are attractedto the inflamed area via chemotaxis and can move out of the blood vessels by the processof diapedesis. Natural killer cells are specialized immunesystem cells that can attack pathogens and cause them to destroy themselves. Pathogens undergo cell death known as apoptosis. 

Let's look at chemical mediators next. Interferons are examples of chemical mediators. Interferons are proteins that interfere orinhibit viral replication. Some white blood cells respond to viral infectionby producing interferons. The infected cell dies and releases the interferon. The interferon can bind to other cells turningon antiviral protein genes. These antiviral proteins then block viralreplication within the cell. 

The complement system is also a form on innateimmunity. The complement system contains 20 plasma proteinsthat, when activated, can kill pathogens. There are 2 ways to activate the complementsystem. One way is through an antibody-antigen connection. This is called the classical pathway and ispart of specific defense. The other is direct activation of the C3 complementprotein by a pathogen. 

This is called the alternative pathway andis a part of innate immunity. The end result of activation of the complementsystem is the formation of membrane attack complexes by activated complement proteins. The membrane attack complexes can tear holesin pathogens disabling and destroying them. Fever is a form on innate immunity as well. 

Body temperature is regulated by the hypothalamus. Chemicals called pyrogens can elevate thetemperature set point in the hypothalamus. As body temperature rises, the liver sequestersiron and zinc which pathogens need to replicate. Fever makes it harder for pathogens to multiply. I hope you have learned something about innateimmunity and see you next time.