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Innate immunity consist in non specific several defense systems and represents the first barrier, always active and without immunological memory.
Cells with this immune function rapidly fight pathogen invasion by destroying these pathogens through phagocytosis phenomenon. This phagocytosis involves many receptors that belong the "Pattern Recognition Receptors" (PRR) family such as Toll-like
, complement receptors
, and lectines
These receptors specifically recognize molecules with highly conserved structural motifs called "Pathogen-Associated Molecular Patterns" (PAMP)
such as LPS
peptidoglycans and lipoteichoic acid (from Gram-positive bacteria), mannose, viral double strand RNA,
CpG motif from bacterial DNA, flagelin, pilin and lipoproteins.
Immune cells involved in innate immunity are :
Besides cells, many molecules are involved in innate immunity like :
Basophils are the least common of the granulocytes, representing about 0.01% to 0.3% of circulating leukocytes (white blood cells).
The proteins and glycoproteins that constitute the complement system are synthesized by the liver hepatocytes.
Complement factor H (CFH) is the major fluid-phase regulator of the alternative pathway of complement. It plays a key role in controlling complement activation in vivo.
Eosinophil granulocytes, usually called eosinophils (or, less commonly, acidophils), are white blood cells that are one of the immune system components responsible for combating infection and parasites in vertebrates. Along with mast cells, they also control mechanisms associated with allergy and asthma. They are granulocytes that develop during Haematopoiesis in the bone marrow before migrating into blood.
Neutrophil granulocytes, generally referred to as neutrophils, are the most abundant type of white blood cells in mammals and form an essential part of the immune system.
Lectins are sugar-binding proteins which are highly specific for their sugar moieties.
Macrophages are white blood cells within tissues, produced by the division of monocytes. Human macrophages are about 21 micrometres in diameter.
A mast cell (or mastocyte) is a resident cell of several types of tissues and contains many granules rich in histamine and heparin. Although best known for their role in allergy and anaphylaxis, mast cells play an important protective role as well, being intimately involved in wound healing and defense against pathogens.
Monocyte is a type of white blood cell, part of the human body's immune system.
Monocytes have two main functions in the immune system: (1) replenish resident macrophages and dendritic cells under normal states, and (2) in response to inflammation signals, monocytes can move quickly (approx. 8-12 hours) to sites of infection in the tissues and divide/differentiate into macrophages and dendritic cells to elicit an immune response. Monocytes are usually identified in stained smears by their large bilobate nucleus.
The Nod-like receptor (NLR) gene family codes for various proteins that contain a central nucleotide binding domain and a series of tandem leucine-rich repeats. NLR proteins are largely thought to serve as pattern recognition receptors (PRRs) which sense microbial products in the cytoplasm of cells, although some members may lack this function.
Scavenger receptors are a group of receptors that recognize modified low density lipoprotein (LDL) by oxidation or acetylation.
Toll-like receptors (TLRs) are a type of pattern recognition receptor (PRR) that play a key role in the adaptive immune system by warning it to the presence of microbial infections.
The innate immune system is an ancient host defense mechanism found in almost every multicellular organism from plants to humans. In invertebrates it is the sole mechanism of defense against pathogens but in higher vertebrates constitutes the first line of defense.
The mannan-binding lectin (MBL) pathway of the complement system is initiated by the binding of MBL or ficolin to specific carbohydrate structures found on the surface of a variety of microorganisms. This binding is followed by the activation of MBL-associated serine proteases (MASPs).