For many years the perception has been that mammalian stress proteins areintracellular molecules that are only present in the extracellular environment as a con-sequence of pathological situations such as necrotic cell death. However, many investiga-tors have now shown that these proteins can be released from a variety of viable(non-necrotic) cell types in vitro, by a mechanism which has yet to be fully established.Moreover, we and a number of others have reported Hsp60 and/or Hsp70 to be presentin the peripheral circulation of normal individuals. These observations have profoundimplications for the perceived role of these proteins as universal pro-inflammatoryintercellular `danger' signalling molecules, and the functional significance and role (s) ofthese ubiquitously expressed and highly conserved families of molecules must thereforebe critically re-evaluated. This paper reviews the evolving evidence which indicates thatstress proteins such as Hsp60 and Hsp70 are present in, and can be released into theextracellular compartment under normal physiological conditions, and puts into contexttheir pro- and anti-inflammatory potential.
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