Innate+Defences

==Innate Defences:== The body is protected from pathogens by the skin and mucous membranes These are all considered to be part of the first line of defence
 * [[file:ucanaandp/Anatomy_The_Skin_-_NCI_Visuals_Online.jpg|Skin ]]is a dead cellular layer that is dry and has a low pH. (see Integumentary )
 * Mucous membranes contain lysozymes (enzymes which break down bacteria) and antibodies
 * Also have hairs, cilia and secretions which help with defence from invaders. For example ciliated cells in the respiratory tract beat upwards pushing mucous with trapped bacteria/viruses etc out of the mouth (mucocillary staircase)
 * Sweat and mucous can actually flush surfaces
 * Stomach - HCl which kills bacteria
 * Urine in theory should flush out the urinary tract.

** Cells **
Non-specific responses are generalised responses to pathogen infection - they do not target a specific cell type

The non-specific response consist of some White Blood Cell's (WBC) and plasma proteins

**__ Phagocytes __**
 * Cells which "eat" foreign material to destroy them
 * Adhere to receptors on target cell membrane
 * Form a vesicle around pathogen
 * Vesicle is full of enzymes which kill the pathogen
 * Phagocytes are formed from stem cells in bone marrow (stem cells are undifferentiated WBC's)

There are 2 classes of phagocytes

__ Microphages __

AND __Macrophages__

Macrophage - "big eaters" phagocytize just about anything. They are all derived from.
 * Can engulf and destroy a pathogen
 * Can destroy by releasing toxins onto pathogens such as NO and H2O2

Macrophages can be of two types.

1) Fixed macrophages - are concentrated in the lungs, liver (Kupffer cells), lining of the lymph nodes and spleen, brain microglia, some kidney cells, and osteoclasts.
 * They are long-lived, depend on mitochondria for energy, and are best at attacking dead cells and pathogens capable of living within cells.
 * Once a macrophage phagocytizes a cell, it places some of its proteins, called epitopes, on its surface - much like a fighter plane displaying its hits.
 * These surface markers serve as an alarm to other immune cells that then infer the form of the invader.
 * All cells that do this are called antigen presenting cells (APCs).

2) The non-fixed or wandering macrophages roam the blood vessels and can even leave them to go to an infection site where they destroy dead tissue and pathogens.   Emigration by squeezing through the capillary walls to the tissue is called diapedesis or extravasation.    The presence of histamines at the infection site attract the cells to their source.    This process is called chemotaxis - ie following a chemical gradient.    Phagocytosis (ref: McKinley and O'Loughlin, Human Anatomy, McGraw Hill)   This is the actual process that many cells use to engulf and destroy foreign particles.


 * 1)  Particle/antigen adhere to the phagocyte
 * 2) Pseudopods engulf the particle (antigen) into a phagosome
 * 3) Phagosomes fuse with a lysosome to form a phagolysosome
 * 4)  Invaders in the phagolysosome are digested by proteolytic enzymes
 * 5)  Indigestible and residual material is removed by exocytosis

Extracellular Killing or Immunological Surveillance
There are a population of cells that constantly monitors the peripheral tissues looking for abnormal cells.

These are Natrual Killer (NK cells). They are a small, distinct group of large granular lymphocytes

Natural Killer cells can lyse and kill cancer and virus infected body cells.

They recognise and respond to a variety of abnormal ‘antigens’ present on abnormal cells

Act by;

• Adhering to target cell • Rotating golgi apparatus to point toward target cell • Produce vesicles with perforins (hole making chemicals) • Perforins make pores (holes) in target cell – lysing it and killing it. • Do not phagocytoses Introduction Innate Defences part 2 Immunity Contents