innate immunity

introduction

innate immunity is a term used to refer to all types of immunity excluding acquired_immunity (acquired immunity relies upon immune cells such as T-cell and B-cell lymphocytes which produce antibodies and these immune systems arose late in evolution, appearing in vertebrates), and thus is relatively non-specific

intact skin and mucosa
desquamation helps remove bacteria
irrigation helps remove organisms
- eg. tears
mucus forms a barrier, traps organisms and allows their expulsion
- in the respiratory tract, mucus expelled via cilia motility mechanisms remove bacteria and fungi
commensal organisms form a normal flora which helps prevent colonisation by more pathogenic flora

an important part of innate immunity is mucus production which forms a barrier to invading organisms
mucus consists of mucins which are glycan sugars and recently, it has been discovered a symbiotic relationship exists whereby certain strains of bacteriophage viruses bind to the mucins and reduce binding of bacteria to the mucin by over 10,000 fold, thereby further reducing bacterial invasion.
- an example is crAssphage which was discovered in 2014 and appears to specifically target Bacteroides sp of bacteria in the gut

see inflammation
cells involved include:
- mast cells
- neutrophils
- eosinophils
- basophils
- macrophages and dendritic cells
- natural killer cells - mainly target intracellular infections
- etc
mechanisms utilise histamine, cytokines, chemokines, etc
- identification of bacteria as pathogens by the innate system usually relies upon the presence of lipopolysaccharide coatings on the bacteria which contain 6 acyl chains that are not too long
phagocytosis of cells is important for intracellular virus or bacterial infections, and xtracellular bacteria and protozoa, but not useful for fungi or intracellular protozoa
coagulation may play a role
some bacteria once inside a macrophage can release toxins to stop the functioning of mitochondria and this then triggers the cell to undergo apoptosis ¹⁾

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