Introduction

Although for many years the perception has been that mammalian heat shock proteins are intracellular molecules that are only released into the extracellular environment in pathological situations such as necrotic cell death, it is now known that these molecules can be released from a variety of viable (non-necrotic) cell types [1–4]. Moreover, we and a number of others have reported Hsp60 and/or Hsp70 to be present in the peripheral circulation of normal individuals [5–12]. These observations have profound implications for the perceived role of these proteins as pro-inflammatory intercellular ‘danger’ signalling molecules and have prompted a re-evaluation of the functional significance and role(s) of these ubiquitously expressed and highly conserved families of molecules. The reader should refer to Chapter 2, which discusses the intracellular dispositions of molecular chaperones and also touches on the release of heat shock proteins, and Chapter 3, in which novel pathways of protein release are described.

The mechanism(s) leading to the release of heat shock proteins are unknown, as is the source of circulating heat shock proteins in the peripheral circulation and their physiological and pathophysiological role(s). The inverse relationship between levels of circulating Hsp70 and the progression of carotid atherosclerosis [13], or the presence of coronary artery disease (CAD) [14], appears to be inconsistent with the concept that this molecule is a danger signal and an in vitro activator of innate and pro-inflammatory immunity [15].