With mouse macrophages, we found that a1m, a2m, and Gc globulin, at concentrations similar to those mea sured in synovial fluid, each dose dependently stimulated the production of TNF, whereas AGP 1, albumin, and haptoglobin did meantime not. The plasma proteins ceruloplasmin, complement component C3, complement component C4, b2 glycoprotein also did not stimulate TNF production. We next examined the effect of a1m, a2m, and Gc globulin on cytokine production in human macrophages. Because the endotoxin LPS is a common contaminant and is itself an agonist of TLR4, we tested the stimula tory properties of the plasma proteins in the presence of polymyxin B, a compound that neutralizes LPS. In the presence of polymyxin B, a1m, Inhibitors,Modulators,Libraries a2m, and Gc globulin induced TNF production was Inhibitors,Modulators,Libraries not significantly reduced, whereas LPS induced TNF production was abrogated.
Additionally, pretreatment with proteinase K significantly abrogated TNF production induced by the plasma proteins but not TNF Inhibitors,Modulators,Libraries production induced by LPS. Although we cannot exclude the possibi lity that a small component of the observed stimulation is due to endotoxin, this result confirms that the plasma proteins are themselves immunostimulatory. Gc globu lin, a1m, and a2m were also able to induce the production of several other inflammatory cytokines that were upregulated in OA serum and synovial fluid, IL 1b, IL 6, and VEGF. Thus, Gc globulin, a1m, and a2m can each induce the produc tion of TNF, IL 1b, IL 6, and VEGF, all molecules impli cated in the pathogenesis of OA.
But how do Inhibitors,Modulators,Libraries these plasma proteins stimulate cytokine production To determine whether these immunostimu latory plasma proteins signal through TLR4, we exam ined whether Gc globulin, a1m, and a2m could also induce TNF production in TLR4 deficient macrophages. TLR4 deficiency inhibited Gc globulin, a1m, and a2m induced TNF production. Confirming that the defect in inflammatory signaling in the Tlr4lps del macro phages was specific to the TLR4 pathway, theTLR2 spe cific agonist peptidoglycan was able to induce TNF production in these cells in fact, to a greater degree than in wild type cells. Thus, Gc globulin, a1m, and a2m induced production of TNF is dependent on TLR4. Interest in the putative immunomodulatory effects of a1m, a2m, and Gc globulin is increasing, with both proinflammatory and antiinflammatory properties sug gested for each of them.
For example, Inhibitors,Modulators,Libraries a1m has been shown to bind to the sur face of various inflammatory cells and to either stimu late or inhibit the activation of human lymphocytes. The immunoregulatory selleck bio role of a1m in health and dis ease is likely to be context dependent. Gc globulin, how ever, appears to be primarily proinflammatory, it enhances the neutrophil and monocyte chemotactic activity of the anaphylatoxin C5a and, in its sialic acid free form, activates macrophages. Here, we uncover an additional mechanism by which these plasma proteins could promote inflammation.