Serum amyloid A1α induces paracrine IL-8/CXCL8 via TLR2 and directly synergizes with this chemokine via CXCR2 and formyl peptide receptor 2 to recruit neutrophils

Abstract

Cell migration depends on the ability of leukocytes to sense an external gradient of chemotactic proteins produced during inflammation. These proteins include chemokines, complement factors, and some acute phase proteins, such as serum amyloid A. Serum amyloid A chemoattracts neutrophils, monocytes, and T lymphocytes via its G protein-coupled receptor formyl peptide receptor 2. We demonstrate that serum amyloid A1α more potently chemoattracts neutrophils in vivo than in vitro. In contrast to CD14(+) monocytes, no rapid (within 2 h) induction of interleukin-8/CXC chemokine ligand 8 or macrophage-inflammatory protein-1α/CC chemokine ligand 3 was observed in purified human neutrophils after stimulation of the cells with serum amyloid A1α or lipopolysaccharide. Moreover, interleukin-8/CXC chemokine ligand 8 induction in monocytes by serum amyloid A1α was mediated by toll-like receptor 2 and was inhibited by association of serum amyloid A1α with high density lipoprotein. This indicates that the potent chemotactic response of neutrophils toward intraperitoneally injected serum amyloid A1α is indirectly enhanced by rapid induction of chemokines in peritoneal cells, synergizing in a paracrine manner with serum amyloid A1α. We observed direct synergy between IL-8/CXC chemokine ligand 8 and serum amyloid A1α, but not lipopolysaccharide, in chemotaxis and shape change assays with neutrophils. Furthermore, the selective CXC chemokine receptor 2 and formyl peptide receptor 2 antagonists, SB225002 and WRW4, respectively, blocked the synergy between IL-8/CXC chemokine ligand 8 and serum amyloid A1α in neutrophil chemotaxis in vitro, indicating that for synergy their corresponding G protein-coupled receptors are required. Additionally, SB225002 significantly inhibited serum amyloid A1α-mediated peritoneal neutrophil influx. Taken together, endogenous (e.g., IL-1β) and exogenous (e.g., lipopolysaccharide) inflammatory mediators induce primary chemoattractants such as serum amyloid A that synergize in an autocrine (monocyte) or a paracrine (neutrophil) fashion with secondary chemokines induced in stromal cells.

Serum amyloid A: an ozone‐induced circulating factor with potentially important functions in the lung‐brain axis

“…One example of such a factor is CXCL1/KC (49). In vitro and in vivo studies using recombinant forms of A-SAA suggest that SAA could contribute to leukocyte trafficking to the airway and other tissues via interactions with scavenger receptors, such as FPR2 (39,74,75). Subchronic O 3 exposure in mice induces the expression of SAA3 in the lungs, which is associated with IL-6-and IL-17A-dependent neutrophil recruitment (39).…”

Structure and Expression of Different Serum Amyloid A (SAA) Variants and their Concentration-Dependent Functions During Host Insults

“…The association between SAA and HDL in the blood circulation could hamper the chemotactic and the cytokine inducing capacities of SAA. Although its chemotactic effect seems to be affected even at high SAA/HDL molar ratios, as observed during an acute phase response, SAA still induces cytokines and chemokines at the same high molar ratios, but this activity decreases as SAA/HDL molar ratios diminish [115, 116, 119, 155]. However, this subject requires further investigation, since contradictory reports exist [118, 126].…”

“…Another theory concerning the inflammatory role of SAA is that it functions (at extremely low concentrations) as a signal relay by inducing chemokines. SAA induces several CC and CXC chemokines, such as CCL2, CCL3 and CXCL8 [116-118], which transmit the chemotactic message to surrounding tissues, extending its action to recruit leukocytes to sites of inflammation [240]. …”

“…More CXCL8 was induced when stimulating synovial fibroblasts or neutrophils with rSAA than with rSAA1α. We also compared both recombinant SAA variants in chemotaxis experiments, but no significant difference in their chemotactic potency for monocytes and neutrophils was found [116, 117]. Furthermore, various A-SAA subtypes were expressed in E. coli and their chemotactic and cytokine inducing capacities were compared by Chen et al [174].…”

“…In contrast to rSAA, SAA purified from patients with high serum SAA titers or SAA-rich plasma were neither able to induce CXCL8, nor to activate neutrophils [242, 244]. Binding of endogenous SAA to HDL may be responsible for the loss of activity of the acute phase protein [116]. In contrast, HDL-associated recombinant SAA was capable of inducing IL-1β and IL-1RA in THP-1 cells, similar to synthetic SAA1α, not associated with HDL [126].…”