Monocyte cytokine synthesis in response to extracellular cell stress proteins suggests these proteins exhibit network behaviour

Human peripheral blood monocytes were exposed to single or pairs of cell stress proteins (CSPs), specifically Hsp10, Hsp27, Hsp60 and Hsp70-the former two having anti-inflammatory actions while the latter pair being assumed to be pro-inflammatory in activity. This study was to test if these proteins exhibited any network behaviour. To control for possible lipopolysaccharide contamination, polymyxin B was used. Surprisingly, at concentrations higher than 1 μg/ml, polymyxin B itself could induce cytokine synthesis. A number of commercial sources of the molecular chaperones were tested, and marked variations in monocyte cytokine synthesis were found. All four CSPs stimulated the same profile of IL-1/IL-6 synthesis and IL-10/TNF-α synthesis although the kinetics of production of these two pairs of cytokines were very different. A key question was whether extracellular molecular chaperones exhibited network behaviour. To test this, monocytes were cultured with suboptimal concentrations of single CSP and pairs of CSP to look for additive, synergistic or antagonistic cell responses. The major finding was that pairs of molecular chaperones, including chaperones thought to stimulate monocyte cytokine synthesis, could produce significant antagonistic cellular responses. This demonstrates that extracellular CSPs constitute an additional potent layer within the complex cytokine network and furthermore suggests that monocytes have evolved to dampen their immune responses upon exposure to extracellular networks of CSPs-perhaps as a mechanism for protecting cells against detrimental cellular stress responses.

Do reciprocal interactions between cell stress proteins and cytokines create a new intra-/extra-cellular signalling nexus?

Cytokine biology began in the 1950s, and by 1988, a large number of cytokines, with a myriad of biological actions, had been discovered. In 1988, the basis of the protein chaperoning function of the heat shock, or cell stress, proteins was identified, and it was assumed that this was their major activity. However, since this time, evidence has accumulated to show that cell stress proteins are secreted by cells and can stimulate cellular cytokine synthesis with the generation of pro- and/or anti-inflammatory cytokine networks. Cell stress can also control cytokine synthesis, and cytokines are able to induce, or even inhibit, the synthesis of selected cell stress proteins and may also promote their release. How cell stress proteins control the formation of cytokines is not understood and how cytokines control cell stress protein synthesis depends on the cellular compartment experiencing stress, with cytoplasmic heat shock factor 1 (HSF1) having a variety of actions on cytokine gene transcription. The endoplasmic reticulum unfolded protein response also exhibits a complex set of behaviours in terms of control of cytokine synthesis. In addition, individual intracellular cell stress proteins, such as Hsp27 and Hsp90, have major roles in controlling cellular responses to cytokines and in controlling cytokine synthesis in response to exogenous factors. While still confusing, the literature supports the hypothesis that cell stress proteins and cytokines may generate complex intra- and extra-cellular networks, which function in the control of cells to external and internal stressors and suggests the cell stress response as a key parameter in cytokine network generation and, as a consequence, in control of immunity.