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*IL-5- stimulates eosinophil growth and differentiation
*IL-5- stimulates eosinophil growth and differentiation
*IL-10- suppresses macrophage functions
*IL-10- suppresses macrophage functions
Although neutrophils produce a lower amount of cytokines per cell than other immune cell types, they are often the first and most common cell type present at sites of infection. This makes them a physiologically important source of cytokines, such as IL-12.
Although neutrophils produce a lower amount of cytokines per cell than other immune cell types, they are often the first and most common cell type present at sites of infection. This makes them a physiologically important source of cytokines, such as IL-12.
==Chemokines==
The chemokines are a superfamily of cytokines, all related in terms of sequence and gene structure. The family is also known as the 'small cytokine' family (scy) or the intercrines. All have a relatively small molecular weight of ~5-10kDa and can be divided in one of two groups based on the position of the cystein residues (important for the tertiary structure):
*C-C subgroup- cysteine residues are adjacent to each other. Important members include:
**Interleukin 8
**MGSA- melanoma growth stimulatory activity
**PF4- platelet factor 4
**βTG- β-thromboglobulin
*C-X-C subgroup- residues are separated by another amino acid. Important members include:
**MCAF- macrophage chemotactic and activating factor
**RANTES
**LD-8
**ACT-2
Chemokines are released by many cell types, and are present in the earliest phase of infection, with actions including the following:
*Lymphoid trafficking
*Wound healing
*Th1/Th2 development
*Angiogenesis/angiostasis
*Lymphoid organ development
*Inflammation
*Cell recruitment
==Cytokines in pathology==
===Bacterial septic shock===
This is the overproduction of cytokines developing a few hours after infection by certain Gram-negative bacteria, including:
*''E. coli''
*''K. pneumoniae''
*''P. aeruginosa''
*''E. aerogenes''
Bacterial cell wall endotoxins are the cause of septic shock, stimulating macrophages to release IL-1 and TNF-α at excessive levels. The condition is often fatal and symptoms include a sudden drop in blood pressure, fever, diarrhoea and blood-clotting in multiple organs.
===Bacterial toxic shock===
This condition is caused by bacterial toxins known as superantigens (antigens that bind simultaneously to MHC II and the beta-V domain of the T cell receptor) that activate large numbers of T cells despite specificity. A number of bacteria have been implicated in the production of superantigens, including:
*''S. aureus''- produces enterotoxins and toxic-shock syndrome toxin
*''M. arthritidis''
The large number of T cells activated by such toxins (between 5-25% of all T cells, compared to less than 0.01% activated towards conventional antigens) means an excessive amount of cytokines produced, such as IL-1 and TNF. These elevated amounts cause the same systemic reactions as seen in bacterial septic shock.
===Lymphoid and myeloid cancers===
The excessive production of cytokines has been linked to some types of cancer, e.g. IL-6 has been shown to be secreted by myeloma cells, plasmacytoma cells and cervical and bladder cancer cells. IL-6 is known to act in an autocrine manner to stimulate cell proliferation.