Antinociceptive effect of the calcium-binding protein MRP-14 and the role played by neutrophils on the control of inflammatory pain.

Macrophages secrete a variety of chemical mediators that play a central role in the pathophysiology of inflammatory pain. Therefore, the activation or deactivation of these cells in an inflammatory focus could modulate the intensity of the algogenic response. Based on these premises and on our previous demonstration that the calcium-binding protein MRP-14, highly expressed in neutrophils, deactivates activated macrophages in vitro, we decided to investigate the role of MRP-14 and of neutrophils in the control of inflammatory pain in mice. Our results show that this protein is endowed with antinociceptive activity. When tested in the writhing model it was able to inhibit pain response but did not change the behavior of the animals in the hot plate test. This observation indicates that MRP-14 down-regulates inflammatory but not central pain. Using a model of acute neutrophilic peritonitis induced by glycogen, a close correlation between neutrophil migration and antinociception was detected. Surgical adrenalectomy demonstrated that the antinociceptive response induced by glycogen was not due to endogenous liberation of glucocorticoids. The treatment of animals either with a monoclonal antibody anti-MRP-14 or a monoclonal antibody that depletes the animals of neutrophils reverts the antinociceptive response observed in the glycogen-induced peritonitis. These data define the calcium-binding protein MRP-14 as a novel mediator for the control of inflammatory pain and consequently discloses an anti-inflammatory role for the neutrophil.

Epithelioid cells from foreign-body granuloma selectively express the calcium-binding protein MRP-14, a novel down-regulatory molecule of macrophage activation.

The S-100 proteins MRP-8 and MRP-14 are expressed by cells of the myelomonocytic lineage, either alone or simultaneously during certain stages of cellular differentiation. We demonstrate that MRP-14 but not MRP-8 was detected by immunostaining in the cytoplasm of epithelioid cells on the surface of round coverslips implanted for 14 days into the subcutaneous tissue of mice. Using this experimental model, our laboratory has previously shown that epithelioid macrophages are poor phagocytic cells that release a macrophage-deactivating factor (MDF) in short-term cultures. The full chemical characterization of MDF has not been achieved so far. We provide evidence that the calcium-binding protein MRP-14 was also released by epithelioid macrophages in short-term cultures and that its neutralization from the culture medium after addition of monoclonal antibody anti-MRP-14 abolished the MDF activity of the conditioned medium. Purified or recombinant human MRP-14 but not MRP-8 inhibits the respiratory burst of BCG-activated macrophages. Recombinant mouse MRP-14 also down-regulate macrophage activation in vitro, and PMA does not revert the inhibitory effect induced by MRP-14. It is thus concluded that epithelioid cells from foreign-body granuloma express and release MRP-14 in short-term cultures and that this molecule is endowed with MDF activity.