Study On Natural Ligand Of Triggering Receptor Expressed On Myeloid Cells-1

Sepsis, systemic inflammatory response syndrome with infection, is the systemic maladaptive response of the host organism to the invasion of normally sterile tissue, fluid or body cavity by pathogenic or potentially pathogenic microorganisms. Sepsis is identified as a serial systemic response such as fever or hypothermia, leukocytosis or leukopenia, tachycardia, shortness of breath and so on, further development of sepsis could lead to septic shock and multiple organ dysfunction syndrome, and also the common complication of severe trauma, burns, shock or surgery operation. Pathogenesis and pathological process of sepsis has not yet been explained clearly, at present the molecular mechanism was considered that the activation of inflammatory cells after infection produced a variety of proinflammatory cytokines, while proinflammatory cytokines would also lead to the activation of inflammatory cells, the reinforce each other led to cascade of inflammatory and progressively enhanced, systemic spread, caused sepsis eventually.Triggering Receptor Expressed on Myeloid Cells (TREM) -1, discovered by Bouchon in 2000, is a transmembrane receptor of the immunoglobulin superfamily. TREM-1 mainly expressed on the surface of neutrophilic polymorphonuclears (PMNs) and monocytes. TREM-1 expression was strongly upregulated in sepsis patients indicated that TREM-1 has close relationship with sepsis. Some related studies pointed out that as a crucial molecular of inflammatory signal transduction in sepsis, TREM-1 played an important role in occurrence and development of sepsis through the TREM-1/DAP12 signaling pathway. On recognition of the unknown natural ligand(s), TREM-1/DAP12 signalling pathway was activated, while inflammatory responses were amplified. Ligation of TREM-1 leads to sustained secretion of proinflammatory cytokines, inflammatory cell infiltration and enhance neutrophil inflammation-inducing effects. Recently studies edicated to finding natural ligand(s) of TREM-1. However, the identity and occurrence of the natural TREM-1 ligands are so far unknown, impairing the further understanding of the biology of this receptor. Researches found that Staphylococcus aureus and Pseudomonas aeruginosa were common pathogens in samples of sepsis patients. And when incubated with either heat-inactivated Staphylococcus aureus or Pseudomonas aeruginosa, PMNs and monocytes play the same effect as in vivo . TREM-1 and the corresponding inflammatory cytokines such as TNF-αand IL-1βexpression were significantly up-regulated, suggested that TREM-1 ligand may exist on the bacteria. Objective To find the natural ligand(s) of human triggering receptor expressed on myeloid cells-1.Methods PMNs and monocytes from human peripheral blood had been isolated with density gradient centrifugation method, and treated with different methods including standard strains, L-form strains, cell walls and cell wall components of Staphylococcus aureus, Pseudomonas aeruginosa or Mycobacterium tuberculosis for 24h. The transcriptional level of TREM-1 was measured by real-time quantitative polymerase chain reaction (Q-PCR) and TNF-α, IL-1βprotein concentration were measured by enzyme-linked immuno sorbent assay (ELISA).Results 1.When PMNs and monocytes were treated with the standard strains and cell wall of Staphylococcus aureus or Pseudomonas aeruginosa, TREM-1 mRNA expression levels and TNF-α, IL-1βconcentration of culture supernatant upgraded significantly (P<0.05). However, there are no same effects while cells were treated with strains and cell wall of Mycobacterium tuberculosis.2. When treated with cell wall components of Staphylococcus aureus, Pseudomonas aeruginosa, effects were different. When treat with the cell wall polysaccharides of Staphylococcus aureus, the expression levels of TREM-1 mRNA in PMNs increased to3.86±0.20-fold, and the expression levels of TREM-1 mRNA in monocytes increased to 5.15±0.56-fold separately compared with blank control group. When treat with the cell wall polysaccharides of Pseudomonas aeruginosa, the expression levels of TREM-1 mRNA in PMNs increased to 4.03±0.15-fold, and the expression levels of TREM-1 mRNA in monocytes increased to 7.22±0.73-fold separately (P <0.05). TNF-αand IL-1βconcentration of cell culture supernatant of the above groups were also increased significantly compared with blank control group (P <0.05). The effects above all could be attenuated by LP17 (P <0.05). However, there are no significant changes when PMNs and monocytes were treated with others cell wall components of Staphylococcus aureus, Pseudomonas aeruginosa and all cell wall components of Mycobacterium tuberculosis, neither expression levels of TREM-1 mRNA nor protein concentration of cell culture supernatant(P>0.05).3. It was found that the TNF-αand IL-1βconcentration of cell culture supernatant had the same trends as TREM-1 mRNA expression levels (P <0.05).Conclusions The experiment results provide the evidence that the natural ligand(s) of TREM-1 is present at cell wall of bacteria such as Staphylococcus aureus, Pseudomonas aeruginosa. And the natural ligand(s) of TREM-1 might be polysaccharides.