A number of different types of non-neuronal cells including lymphocytes and monocytes possess SP and its specific NK1-R(Marriotte et al., 2001); however, the pathophysiological roles of SP in these cells remain to be established SP promotes platelet-dependent clot formation through NK1-R, in which leukocytes are involved (Azma et al., 2009
). SP triggers functional responses in many cells of the immune system through NK1-R including inflammatory processes and immunologic responses, involving monocytes, macrophages, lymphocytes, microglia, natural killer cells, and precursors of immune cells (Douglas et al., 2011
; Lai et al., 1998
; Ho et al., 2002
; Ho et al., 1997
By stimulating monocytes with SP, we found that TF antigen was expressed () and using TGA revealed it was active (). The time course shows no increase at 2 hours, a minimal increase at 3 hours, a maximum increase at 4 hours, and no increase at 6 hours (). This pattern of responses is similar to the synthesis of TF observed following stimulation of monocytes with bacterial LPS over time.
Peripheral tachykinins and the NK1-R are required for thrombus formation (Jones et al, 2008
). Moreover, blood obtained from the NK1-R–deficient mice produced markedly smaller thrombi with a NK1-R agonist compared with blood from control mice suggesting that physiologically, SP is a major NK1-R agonist responsible for amplifying thrombus formation through the NK1-R (Bozic et al.,1996
). Two naturally occurring variants of the NK1-R mediate the effects of SP: a full length, NK1-RF (407 aa) and a truncated form NK1-RT that lacks 96 amino acid residues at the C-terminus (311 amino acid). We have detected the truncated NK1-R in the non-differentiated monocytic THP-1 cell line and in primary monocytes using RT–PCR. Both full length and truncated forms were detected in the THP-1 cells differentiated into macrophages using PMA (Lai et al., 2006
). The full length variant is capable of signaling, whereas the truncated NK1-R primes the chemokine receptor CCR5 (Chernova et al., 2009
). The potential inhibitory roles of SP antagonist CP-96345 have been described in our laboratory. CP-96345 inhibits HIV (R5 strains) replication in human monocyte-derived macrophages (MDM) in part through the CCR5 receptor as well as through downregulation of other pathways (Lai et al., 2001
). The SP antagonist, CP-96345, but not the inactive enantiomer CP-96344 inhibits TF expression. NK1-R is required for SP-induced monocyte TF expression () which is most likely mediated through NK1-RT, the predominant isoform in monocytes (Douglas et al., 2011
SP activates NF-κB, a factor involved in the control of cytokine expression, and stimulates human peripheral blood mononuclear cells (PBMC) to produce inflammatory cytokines including IL-1, IL-6, TNF-α and IL-12 in HIV-infected patients (Bremer et al., 2010
; Douglas et al., 2011
). Cytokines (GM-CSF, IFNγ, TNF-α) and chemokines (MIP-1α, MIP-1β, RANTES) inhibit HIV-1 by suppressing viral entry and replication (Douglas et al., 2011
). The role of SP on the expression of TF by these agents is unknown. We demonstrate that GM-CSF, IFNγ, TNF-α, MIP-1α, MIP-1β, and RANTES are released from monocytes after stimulated with SP (). We have observed biphasic responses for all of the cytokines (GM-CSF, IFN-γ, TNFα) and chemokines (MIP-1α and MIP-1β) except RANTES in SP stimulated monocytes similar to previous studies where IL-8 and IL-6 mRNA were observed in parainfluenza virus type-4 (PIV-4) infected NCI-H292 cells (Rogers et al., 2004
). In an another study using human whole blood as an ex vivo model of local cytokine production, TNFα, IL-1α, IL-1β, IL-6, and IL-8 were first detected between 1 and 4 hours post –LPS stimulation, and reached plateau levels after 6 to 12 hours (Deforge et al., 1992
In order to determine the effect of chemokines/cytokines on the expression of TF treated with identical concentrations of chemokines and cytokines (released from monocytes after stimulated with SP), we found that chemokines (MIP-1α, MIP-1β, RANTES) failed to express TF on monocytes (). In contrast, stimulation with each of the cytokines leads to TF expression on monocytes ().
The blocking of SP induced TF expression by MAB to TNF-α suggests an indirect autocrine pathway in monocytes that depends on TNF-α (). A similar mechanism was observed on monocyte TF expression by HKa (Khan et al., 2010
). In contrast, SP induced TF expression on monocytes was synergistically augmented even in the presence of MAB against cytokines GM-CSF and IFN-γ (). SP induced TF expression is mediated by TNF-α and not by GM-CSF or IFN-γ. We observed a synergistic effect of each cytokine with SP but only a MAB to TNF-α inhibited TF expression. This finding indicates the possibility of a different receptor or signaling pathway through which GM-CSF and IFN-γ expresses monocyte TF.
In summary, we have demonstrated that SP triggers TF synthesis on monocytes in a time and concentration dependent manner. NK1-R is the most critical receptor for SP-induced TF expression. SP induced TF expression was mediated by TNFα in an autocrine pathway. NK1-R may be a new and potential therapeutic target in the treatment of vaso-occlusive disorders.