Nef protein of human immunodeficiency virus and lipopolysaccharide induce expression of CD14 on human monocytes through differential utilization of interleukin-10

An Autoimmune Disease-Associated Risk Variant in the TNFAIP3 Gene Plays a Protective Role in Brucellosis That Is Mediated by the NF-κB Signaling Pathway

Naturally occurring functional variants (rs148314165 and rs200820567, collectively referred to as TT>A) reduce the expression of the tumor necrosis factor alpha-induced protein 3 (TNFAIP3) gene, a negative regulator of NF-κB signaling, and predispose individuals to autoimmune disease. In this analysis, we conducted a genetic association study of the TT>A variants in 1,209 controls and 150 patients with brucellosis, an infectious disease, and further assessed the role of the variants in brucellosis. Our data demonstrated that the TT>A variants were correlated with cases of brucellosis (P = 0.002; odds ratio [OR] = 0.34) and with individuals who had a positive serum agglutination test (SAT) result (titer of >1/160) (P = 4.2 × 10⁻⁶; OR = 0.23). A functional study demonstrated that brucellosis patients carrying the protective allele (A) showed significantly lower expression levels of the TNFAIP3 gene in their peripheral blood mononuclear cells and showed increased NF-κB signaling. Monocytes from individuals carrying the A allele that were stimulated with Brucella abortus had lower mRNA levels of TNFAIP3 and produced more interleukin-10 (IL-10), IL-6, and IL-1β than those from TT allele carriers. These data showed that autoimmune disease-associated risk variants, TT>A, of the TNFAIP3 locus play a protective role in the pathogenesis of brucellosis. Our findings suggest that a disruption of the normal function of the TNFAIP3 gene might serve as a therapeutic target for the treatment of brucellosis.

Brucella Dysregulates Monocytes and Inhibits Macrophage Polarization through LC3-Dependent Autophagy

Brucellosis is caused by infection with Brucella species and exhibits diverse clinical manifestations in infected humans. Monocytes and macrophages are not only the first line of defense against Brucella infection but also a main reservoir for Brucella. In the present study, we examined the effects of Brucella infection on human peripheral monocytes and monocyte-derived polarized macrophages. We showed that Brucella infection led to an increase in the proportion of CD14⁺⁺CD16⁻ monocytes and the expression of the autophagy-related protein LC3B, and the effects of Brucella-induced monocytes are inhibited after 6 weeks of antibiotic treatment. Additionally, the production of IL-1β, IL-6, IL-10, and TNF-α from monocytes in patients with brucellosis was suppressed through the LC3-dependent autophagy pathway during Brucella infection. Moreover, Brucella infection inhibited macrophage polarization. Consistently, the addition of 3-MA, an inhibitor of LC3-related autophagy, partially restored macrophage polarization. Intriguingly, we also found that the upregulation of LC3B expression by rapamycin and heat-killed Brucella in vitro inhibits M2 macrophage polarization, which can be reversed partially by 3-MA. Taken together, these findings reveal that Brucella dysregulates monocyte and macrophage polarization through LC3-dependent autophagy. Thus, targeting this pathway may lead to the development of new therapeutics against Brucellosis.

A responsive human triple-culture model of the air-blood barrier: incorporation of different macrophage phenotypes

Current pulmonary research underlines the relevance of the alveolar macrophage (AM) integrated in multicellular co-culture-systems of the respiratory tract to unravel, for example, the mechanisms of tissue regeneration. AMs demonstrate a specific functionality, as they inhabit a unique microenvironment with high oxygen levels and exposure to external hazards. Healthy AMs display an anti-inflammatory phenotype, prevent hypersensitivity to normally innocuous contaminants and maintain tissue homeostasis in the alveolus. To mirror the actual physiological function of the AM, we developed three different polarized [classically activated (M1) and alternatively activated (M2_wh , wound-healing; M2_reg , regulatory)] macrophage models using a mixture of differentiation mediators, as described in the current literature. To test their immunological impact, these distinct macrophage phenotypes were seeded on to the epithelial layer of an established in vitro air-blood barrier co-culture, consisting of alveolar epithelial cells A549 or H441 and microvascular endothelial cells ISO-HAS-1 on the opposite side of a Transwell filter-membrane. IL-8 and sICAM release were measured as functionality parameters after LPS challenge. The M1 model itself already provoked a severe inflammatory-like response of the air-blood barrier co-culture, thus demonstrating its potential as a useful in vitro model for inflammatory lung diseases. The two M2 models represent a 'non-inflammatory' phenotype but still showed the ability to trigger inflammation following LPS challenge. Hence, the latter could be used to establish a quiescent, physiological in vitro air-blood model. Thus, the more complex differentiation protocol developed in the present study provides a responsive in vitro triple-culture model of the air-blood-barrier that mimics AM features as they occur in vivo. © 2015 The Authors Journal of Tissue Engineering and Regenerative Medicine Published by John Wiley & Sons, Ltd.

Intracellular overexpression of HIV-1 Nef impairs differentiation and maturation of monocytic precursors towards dendritic cells

Nef functions as an immunosuppressive factor critical for HIV-1 replication, survival and development of AIDS following HIV-1 infection. What effects Nef exerts on differentiation and maturation of monocytes towards dendritic cells (DCs) remains greatly controversial. In this study, we used THP-1 (human monocytic leukemia cell line) as monocytic DC precursors to investigate how overexpression of HIV-1 Nef influences the processes of differentiation and maturation of dendritic cells. In striking contrast to negative controls, our results showed that morphological and phenotypical changes (CD11c, CD14, CD40, CD80, CD83, CD86, and HLA-DR) occurred on recombinant THP-1 expressing HIV-1 Nef (short for Nef) upon co-stimulation of GM-CSF/IL-4 or GM-CSF/IL-4/TNF-α/ionomycin. Moreover, CD4, CCR5, and CXCR4 were also down-regulated on Nef. It might be hypothesized that Nef prevents superinfection and signal transduction in HIV-1 infected monocytes. Collectively, our study demonstrates that long-lasting expression of Nef at high levels indeed retards differentiation and maturation of dendritic cells in terms of phenotype and morphology. We are hopeful that potentially, stable expression of intracellular Nef in vivo may function as a subtle mode to support long-lasting HIV-1 existence.

The macrophage in HIV-1 infection: from activation to deactivation?

Macrophages play a crucial role in innate and adaptative immunity in response to microorganisms and are an important cellular target during HIV-1 infection. Recently, the heterogeneity of the macrophage population has been highlighted. Classically activated or type 1 macrophages (M1) induced in particular by IFN-γ display a pro-inflammatory profile. The alternatively activated or type 2 macrophages (M2) induced by Th-2 cytokines, such as IL-4 and IL-13 express anti-inflammatory and tissue repair properties. Finally IL-10 has been described as the prototypic cytokine involved in the deactivation of macrophages (dM). Since the capacity of macrophages to support productive HIV-1 infection is known to be modulated by cytokines, this review shows how modulation of macrophage activation by cytokines impacts the capacity to support productive HIV-1 infection. Based on the activation status of macrophages we propose a model starting with M1 classically activated macrophages with accelerated formation of viral reservoirs in a context of Th1 and proinflammatory cytokines. Then IL-4/IL-13 alternatively activated M2 macrophages will enter into the game that will stop the expansion of the HIV-1 reservoir. Finally IL-10 deactivation of macrophages will lead to immune failure observed at the very late stages of the HIV-1 disease.

HIV-1 Nef inhibits lipopolysaccharide-induced IL-12p40 expression by inhibiting JNK-activated NFkappaB in human monocytic cells

Impaired cellular immunity caused by decreased production of Th1-type cytokines, including interleukin-12 (IL-12) is a major feature of HIV-1-associated immunodeficiency and acquired immunodeficiency syndrome. IL-12p40, an inducible subunit shared between IL-12 and IL-23, plays a critical role in the development of cellular immunity, and its production is significantly decreased during HIV infection. The mechanism by which HIV induces loss of IL-12p40 production remains poorly understood. We have previously shown that lipopolysaccharide (LPS)-induced IL-12p40 production in monocytic cells is regulated by NFkappaB and AP-1 transcription factors through the activation of two distinct upstream signaling pathways, namely the c-Jun-N-terminal kinase (JNK) and the calmodulin-dependent protein kinase-II-activated pathways. Herein, we show that intracellular nef expressed through transduction of primary monocytes and promonocytic THP-1 cells with retroviral-mediated nef gene inhibited LPS-induced IL-12p40 transcription by inhibiting the JNK mitogen-activated protein kinases without affecting the calmodulin-dependent protein kinase-II-activated pathway. In addition, nef inhibited JNK-activated NFkappaB without affecting the AP-1 activity. Overall, our results suggest for the first time that intracellular nef inhibited LPS-activated JNK, which may cause inhibition of IL-12p40 expression in human monocytic cells by selectively inhibiting NFkappaB activity.

IL-10 regulation by HIV-Tat in primary human monocytic cells: involvement of calmodulin/calmodulin-dependent protein kinase-activated p38 MAPK and Sp-1 and CREB-1 transcription factors

The anti-inflammatory cytokine, IL-10 plays an important role in HIV immunopathogenesis. The HIV accessory protein, Tat is not only critical for viral replication, but affects the host immune system by influencing cytokine production including IL-10. During HIV infection, IL-10 production by monocytic cells is up-regulated, representing a critical pathway by which HIV may induce immunodeficiency. Herein, we show that extracellular Tat-induced IL-10 expression in normal human monocytes. To understand the signaling pathways underlying HIV-Tat induced IL-10 transcription, we investigated the involvement of MAPK as well as calcium signaling and the downstream transcription factor(s). Our results suggest that Tat-induced calcium influx regulated IL-10 transcription in monocytic cells. The experiments designed to further understand the molecules involved in the calcium signaling suggested that calmodulin and calmodulin-dependent protein kinase-II (CaMK-II)-activated p38 MAPK played a role in extracellular Tat-induced IL-10 expression in primary human monocytes. Furthermore, Tat-induced IL-10 expression was regulated by p38 MAPK- and CaMK II-activated CREB-1 as well as Sp-1 transcription factors. Taken together, our results suggest that extracellular HIV-Tat induced IL-10 transcription in primary human monocytes is regulated by CREB-1 and Sp-1 transcription factors through the activation of calmodulin/CaMK-II-dependent p38 MAPK.

STAT-1 mediates the stimulatory effect of IL-10 on CD14 expression in human monocytic cells

IL-10, an anti-inflammatory cytokine, has been shown to exhibit stimulatory functions including CD14 up-regulation on human monocytic cells. CD14-mediated signaling following LPS stimulation of monocytic cells results in the synthesis of proinflammatory cytokines. Our results show that LPS-induced CD14 expression on monocytic cells may be mediated by endogenously produced IL-10. To investigate the molecular mechanism by which IL-10 enhances CD14 expression, both human monocytes and the promyelocytic HL-60 cells were used as model systems. IL-10 induced the phosphorylation of PI3K and p42/44 ERK MAPK. By using specific inhibitors for PI3K (LY294002) and ERK MAPKs (PD98059), we demonstrate that LY294002 either alone or in conjunction with PD98059 inhibited IL-10-induced phosphorylation of STAT-1 and consequently CD14 expression. However, IL-10-induced STAT-3 phosphorylation remained unaffected under these conditions. Finally, STAT-1 interfering RNA inhibited IL-10-induced CD14 expression. Taken together, these results suggest that IL-10-induced CD14 up-regulation in human monocytic cells may be mediated by STAT-1 activation through the activation of PI3K either alone or in concert with the ERK MAPK.

Long-distance running modulates the expression of leucocyte and endothelial adhesion molecules

There still exist many unanswered questions whether physical exercise is beneficial or harmful to the immune system. The 'open-window' post-exercise hypothesis states that athletes are more susceptible to infections after exercise, but there is a need for further elucidation. The aim of the present study was to investigate the effect of long-distance running on leucocyte expression of selected adhesion molecules as well as the plasma levels of soluble leucocyte- and endothelium-derived adhesion molecules. Twenty-seven men participating in Oslo marathon together with 16 entrants (eight men and eight women) in the Oslo half-marathon were recruited to this study. Venous blood was collected before and immediately after the races for analysing the leucocyte expression of CD62L, CD11b and CD14 with the help of flow cytometry, and plasma concentrations of soluble (s) sE-selectin, sL-selectin, sP-selectin, sVCAM-1, sICAM-1 and sCD14 were assessed by means of enzyme-linked immunosorbent assays. A significant increase of leucocyte CD11b expression was observed following both races, compared to the pre-race situation. Monocyte CD14 expression increased only after the marathon race. After both races, CD62L expression was significantly lowered on all leucocyte subsets, whereas the plasma levels of sE-selectin, sP-selectin, sL-selectin, sVCAM-1, sICAM-1 and sCD14 were all increased. Altogether, these changes negatively influence the ability of leucocytes to adhere to and actively transmigrate the endothelium to reach the tissues. Our study thus supports the 'open-window' hypothesis, indicating a reduced capacity to combat infectious agents during the immediate post-exercise period.