HSP27: an anti-inflammatory and immunomodulatory stress protein acting to dampen immune function

The effects of HSP27 on human monocytes (MO) are predominantly antiinflammatory through preferential interleukin (IL)10 induction and by alteration of MO to immature dendritic cells (iDCs) or MO to macrophage (Mac) differentiation. Initial HSP27 inclusion in IL4+GM-CSF MO to iDC induction cultures allows Mac differentiation (CD14++, CD16+), decreases iDC (CD1a+) differentiation, and depresses DC induction of allogeneic T lymphocyte proliferation (MLR). HSP27 increased MO IL10 and M-CSF production but subsequent increased Mac differentiation isn't responsible for depressed MO to iDC differentiation and function. Mac function after IL10 induced MO to Mac differentiation is also altered by HSP27 inclusion so that Mac phagocytic activity and scavenger receptor expression (CD163) are depressed. HSP27, in addition to immature DCs, doesn't increase Mac differentiation but instead generates inhibitory DCs, which depress rather than stimulate T cell proliferation even during anti CD3+CD28 induction. Upon maturation, these HSP27-altered inhibitory DCs have increased production of the T cell and DC suppressive mediator, thrombospondin 1. HSP27's anti-inflammatory and immunodepressive effects include deranging MO differentiation to both Mac and DCs, altering their receptor expression, and inducing production of inhibitory mediators such as thrombospondin-1 as well as IL10. These data suggest HSP27 belongs to a new group of 'anti-danger signals'.