Interstitial fluid, immunoglobulin

Extracellular antigens are detected by APCs, such as lymphocytes, macrophages, and dendritic cells in interstitial fluid and blood. These detect the hapten and engulf the whole antigenic complex. Then, when inside the APC, the complex is partly dismantled and peptides attached to proteins similar to immunoglobulins, known as MHC II. The modified peptide-hapten complex is moved to the surface of the APC and presented as a complex with MHC to T-helper cells (CD4+), which activates and instructs the APC to make antibodies to the hapten and also B cells (memory cells with "memory" of the hapten) to proliferate. These events lead to types I to III responses. 

A single individual may produce a population of antibody specificities, an antibody repertoire, which is a reflection of all the B cell clones (lymphocyte repertoire) capable of immunoglobulin (Ig) synthesis and secretion in response to antigenic stimulation, but also in absence of exposure to environmental pathogens [48, 49]. Natural antibodies, in fact, are germ line-encoded molecules produced by a distinct population of peritoneal B cells, bearing the cell surface marker CD 5 and are present in the sera and interstitial fluids of healthy individuals [49-51]. 

Once egress from plasma is accomplished, IgG is the most abundant immunoglobulin in tissue and is particularly prominent in the interstitial fluid compartment [2], In healthy adult human volunteers, dermal interstitial fluid endogenous IgG levels were demonstrated to be 30% of plasma IgG levels [59]. In mice, IgG transport from capillary beds into interstitium is most frequent in skin and muscle with equivalent or less transport in adipose tissue and liver and much less transport in other tissues [60-62] consistent with the... 

Olszewski WL, Engeset A. Capillary transport of immunoglobulins and complement proteins to the interstitial fluid and lymph. Arch Immunol Ther Exp (Warsz) 1978 26(l-6) 57-65. 

The primary functions of albumin are to help maintain the osmotic (oncotic) transmural pressure differential that ensures proper mass exchange between blood and interstitial fluid at the capillary level and to serve as a transport carrier molecule for several hormones and other small biochemical constituents (such as some metal ions). The primary function of the globulin class of proteins is to act as transport carrier molecules (mostly of the a and p class) for large biochemical substances, such as fats (lipoproteins) and certain carbohydrates (muco- and glycoproteins) and heavy metals (mineraloproteins), and to work together with leukocytes in the body s immune system. The latter function is primarily the responsibflity of the y class of immunoglobulins, which have antibody activity. The primary function of fibrinogen is to work with thrombocytes in the formation of a blood clot — a process also aided by one of the most abundant of the lesser proteins, prothrombin (MW 62,000). 

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