Sphingosine-1-phosphate (S1P) is a lipid mediator involved in many processes, including development of vessels, vascular permeability, and immune function. It is found in the blood, often bound with proteins such as high density lipoprotein (HDL, “good cholesterol”). Receptors for S1P are found on many cell types.
Activation of the high affinity receptor for IgE causes production of S1P by mast cells. This may also affect the expression and activation of S1P receptors. Mast cells then secrete S1P into the surrounding space. Mast cells also have receptors to bind S1P.
The S1P1 receptor helps to direct mast cells to sites of inflammation, but does not influence degranulation. The S1P2 receptor deters from localizing to sites of inflammation but enhances degranulation once they have migrated. S1P is known to increase during acute tissue inflammation, in airways following asthmatic challenge and in joints of rheumatic patients. S1P may be responsible for the accumulation of immune cells in such places, but the exact nature of this role is unclear.
S1P receptors regulate the vascular system, including heart rate and permeability. S1P2 receptor makes vessels more permeable and regulates blood flow to various organs. S1P2 receptor is involved in counteracting the vasodilation effect of histamine (and thus low blood pressure). Histamine can stimulate S1P production.
S1P can also cause bradycardia and high blood pressure via the S1P3 receptor. I am curious to know if S1P is involved in the high blood pressure type of anaphylaxis some people have.
In models where the genes for making S1P have been deleted, recovery from anaphylaxis is delayed, with severe hypotension. However, in mice with S1P2 receptors, injecting S1P could rescue mice from anaphylaxis. For this reason, molecules that can act on the S1P receptors are being investigated as possible drug targets to produce an alternative to epinephrine.
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Olivera A, Eisner C, Kitamura Y, et al. Sphingosine kinase 1 and sphingosine-1-phosphate receptor 2 are vital to recovery from anaphylactic shock. J Clin Invest. 2010 “in press”.