Expression of the common heat-shock protein receptor CD91 is increased on monocytes of exposed yet HIV-1-seronegative subjects

Role of HIV-1 Tat Protein Interactions with Host Receptors in HIV Infection and Pathogenesis

Each time the virus starts a new round of expression/replication, even under effective antiretroviral therapy (ART), the transactivator of viral transcription Tat is one of the first HIV-1 protein to be produced, as it is strictly required for HIV replication and spreading. At this stage, most of the Tat protein exits infected cells, accumulates in the extracellular matrix and exerts profound effects on both the virus and neighbor cells, mostly of the innate and adaptive immune systems. Through these effects, extracellular Tat contributes to the acquisition of infection, spreading and progression to AIDS in untreated patients, or to non-AIDS co-morbidities in ART-treated individuals, who experience inflammation and immune activation despite virus suppression. Here, we review the role of extracellular Tat in both the virus life cycle and on cells of the innate and adaptive immune system, and we provide epidemiological and experimental evidence of the importance of targeting Tat to block residual HIV expression and replication. Finally, we briefly review vaccine studies showing that a therapeutic Tat vaccine intensifies ART, while its inclusion in a preventative vaccine may blunt escape from neutralizing antibodies and block early events in HIV acquisition.

Toll-like Receptor Response to Human Immunodeficiency Virus Type 1 or Co-Infection with Hepatitis B or C Virus: An Overview

Toll-like receptors (TLRs) are evolutionarily conserved pattern recognition receptors that play important roles in the early detection of pathogen-associated molecular patterns and shaping innate and adaptive immune responses, which may influence the consequences of infection. Similarly to other viral infections, human immunodeficiency virus type 1 (HIV-1) also modulates the host TLR response; therefore, a proper understanding of the response induced by human HIV-1 or co-infection with hepatitis B virus (HBV) or hepatitis C virus (HCV), due to the common mode of transmission of these viruses, is essential for understanding HIV-1 pathogenesis during mono- or co-infection with HBV or HCV, as well as for HIV-1 cure strategies. In this review, we discuss the host TLR response during HIV-1 infection and the innate immune evasion mechanisms adopted by HIV-1 for infection establishment. We also examine changes in the host TLR response during HIV-1 co-infection with HBV or HCV; however, this type of study is extremely scarce. Moreover, we discuss studies investigating TLR agonists as latency-reverting agents and immune stimulators towards new strategies for curing HIV. This understanding will help develop a new strategy for curing HIV-1 mono-infection or co-infection with HBV or HCV.

Multi-faceted role of LRP1 in the immune system

Graft versus host disease (GVHD) represents the major complication after allogeneic hematopoietic stem cell transplantation (Allo-SCT). GVHD-prone patients rely on GVHD prophylaxis (e.g. methotrexate) and generalized anti-GVHD medical regimen (glucocorticoids). New anti-GVHD therapy strategies are being constantly explored, however there is an urgent need to improve current treatment, since GVHD-related mortality reaches 22% within 5 years in patients with chronic GVHD. This review is an attempt to describe a very well-known receptor in lipoprotein studies - the low-density lipoprotein receptor related protein 1 (LRP1) - in a new light, as a potential therapeutic target for GVHD prevention and treatment. Our preliminary studies demonstrated that LRP1 deletion in donor murine T cells results in significantly lower GVHD-related mortality in recipient mice with MHC (major histocompatibility complex) -mismatched HSCT. Given the importance of T cells in the development of GVHD, there is a significant gap in scientific literature regarding LRP1's role in T cell biology. Furthermore, there is limited research interest and publications on this classical receptor molecule in other immune cell types. Herein, we endeavor to summarize existing knowledge about LRP1's role in various immune cells to demonstrate the possibility of this receptor to serve as a novel target for anti-GVHD treatment.

LRP1/CD91 is highly expressed in monocytes from patients with vitiligo - even after repigmentation

Vitiligo pathophysiology is mediated by antigen-specific cytotoxic T cells. Environmental stressors cause susceptible melanocytes to secrete damage-associated molecular patterns (DAMPs). DAMPs are recognized by receptors such as the endocytic low-density lipoprotein receptor-related protein (LRP1/CD91), expressed in antigen-presenting cells, which activate self-reactive CD8+ T cells, leading to melanocyte destruction. Within this response, interferon gamma triggers production of cytokine CXCL10, recruiting more activated T cells causing further melanocytic damage. We hypothesized that expression of LRP1/CD91 was higher in vitiligo patients compared to non-vitiligo individuals. And further that levels/expression of CXCL10 in plasma were linked to disease severity. We enrolled forty individuals in this study: 18 patients with vitiligo and 22 healthy volunteers. We assessed LRP1/CD91 expression and plasma CXCL10 in patients with vitiligo and healthy volunteers. Additionally, vitiligo patients received combined treatment for 16 weeks following which the said parameters were reassessed. Vitiligo Area Scoring Index was calculated before and after treatment for these patients. Analysis of LRP1/CD91 MFI values in monocytes from vitiligo patients showed high surface levels of LRP1/CD91 than from healthy volunteers (10.50 ± 0.77 vs. 6.55 ± 0.77 MFI units, p < 0.001). This expression did not change after treatment. Plasma levels of CXCL10 were higher in vitiligo patients than healthy volunteers (93.78 ± 7.73 vs. 40.17 ± 6.25 pg/ml). The patients with a good clinical response to treatment had a parallel reduction in plasma CXCL10 levels (105.8 ± 18.44 vs. 66.13 ± 4.87 pg/ml) before and after treatment. LRP1/CD91 expression may reflect susceptibility to vitiligo. Plasma levels of CXCL10 can represent a biomarker for monitoring treatment response. LRP1 and CXCL10 may represent therapeutic targets.

Bright expression of CD91 identifies highly activated human dendritic cells that can be expanded by defensins

CD91 is a scavenger receptor expressed by different immune cells and its ligands defensins have been demonstrated to contribute to immune responses against infections and tumours. We previously demonstrated that CD91 is expressed on human monocyte-derived dendritic cells (moDCs) and that human defensins stimulate in vitro the activation of these cells. In this study, we observed that CD91 is expressed at different levels on two distinct moDC subsets: CD91(dim) and CD91(bright) moDCs. Although CD91(bright) moDCs represented a small proportion of total moDCs, this subset showed higher levels of activation and maturation markers compared with CD91(dim) moDCs. The frequency of CD91(bright) moDCs increased by ~ 50% after in vitro stimulation with recombinant human neutrophil peptide-1 (rHNP-1) and recombinant human β defensin-1 (rHBD-1), while lipopolysaccharide (LPS) stimulation decreased it by ~ 35%. Both defensins up-regulated moDC expression of CD80, CD40, CD83 and HLA-DR, although to a lower extent compared with LPS. Notably, upon culture with rHNP-1 and rHBD-1, CD91(bright) moDCs maintained their higher activation/maturation status, whereas this was lost upon culture with LPS. Our findings suggest that defensins promote the differentiation into activated CD91(bright) DCs and may encourage the exploitation of the CD91/defensins axis as a novel therapeutic strategy to potentiate antimicrobial and anti-tumour immune response.

Properties of human blood monocytes. I. CD91 expression and log orthogonal light scatter provide a robust method to identify monocytes that is more accurate than CD14 expression

BACKGROUND

This study was designed to improve identification of human blood monocytes by using antibodies to molecules that occur consistently on all stages of monocyte development and differentiation.

METHODS

We examined blood samples from 200 healthy adults without clinically diagnosed immunological abnormalities by flow cytometry (FCM) with multiple combinations of antibodies and with a hematology analyzer (Beckman LH750).

RESULTS

CD91 (α2 -macroglobulin receptor) was expressed only by monocytes and to a consistent level among subjects [mean median fluorescence intensity (MFI) = 16.2 ± 3.2]. Notably, only 85.7 ± 5.82% of the CD91(+) monocytes expressed high levels of the classical monocyte marker CD14, with some CD91(+) CD16(+) cells having negligible CD14, indicating that substantial FCM under-counts will occur when monocytes are identified by high CD14. CD33 (receptor for sialyl conjugates) was co-expressed with CD91 on monocytes but CD33 expression varied by nearly ten-fold among subjects (mean MFI = 17.4 ± 7.7). In comparison to FCM analyses, the hematology analyzer systematically over-counted monocytes and eosinophils while lymphocyte and neutrophil differential values generally agreed with FCM methods.

CONCLUSIONS

CD91 is a better marker to identify monocytes than CD14 or CD33. Furthermore, FCM (with anti-CD91) identifies monocytes better than a currently used clinical CBC instrument. Use of anti-CD91 together with anti-CD14 and anti-CD16 supports the identification of the diagnostically significant monocyte populations with variable expression of CD14 and CD16.

LRP1/CD91 is up-regulated in monocytes from patients with haemophilia A: a single-centre analysis

The low-density lipoprotein receptor-related protein 1 (LRP1) is an ubiquitously expressed endocytic receptor that, among its several functions, is involved in the catabolism of coagulation factor VIII (FVIII) and in the regulation of its plasma concentrations. Although LRP1/CD91 polymorphisms have been associated with increased FVIII levels and a consequent thrombotic risk, no data are available on LRP1/CD91 expression in patients with inherited FVIII deficiency. With the aim of elucidating this issue, 45 consecutive patients with haemophilia A (HA) (18 severe, 5 moderate and 22 mild HA) were enrolled in this cross-sectional, single-centre survey. The LRP1/CD91 mean fluorescence intensity (MFI) in monocytes from HA patients was significantly higher than that detected in 90 healthy blood donors (105 vs. 67, P < 0.001). This over-expression was independent of hepatitis C virus infection status and varied according to the severity of the haemophilia, being higher in patients with more severe FVIII deficiency. In conclusion, our study documents for the first time that LRP1/CD91 is over-expressed on monocytes from HA patients, with the intensity of expression varying according to the severity of the FVIII deficiency. Further studies are needed to assess the clinical implications of these findings.

Primary effusion lymphoma cell death induced by bortezomib and AG 490 activates dendritic cells through CD91

To understand how cytotoxic agent-induced cancer cell death affects the immune system is of fundamental importance to stimulate immune response to counteract the high mortality due to cancer. Here we compared the immunogenicity of Primary Effusion Lymphoma (PEL) cell death induced by anticancer drug Bortezomib (Velcade) and Tyrphostin AG 490, a Janus Activated Kinase 2/signal trasducer and activator of transcription-3 (JAK2/STAT3) inhibitor. We show that both treatments were able to induce PEL apoptosis with similar kinetics and promote dendritic cells (DC) maturation. The surface expression of molecules involved in immune activation, namely calreticulin (CRT), heat shock proteins (HSP) 90 and 70 increased in dying cells. This was correlated with DC activation. We found that PEL cell death induced by Bortezomib was more effective in inducing uptake by DC compared to AG 490 or combination of both drugs. However the DC activation induced by all treatments was completely inhibited when these cells were pretreated with a neutralizing antiboby directed against the HSP90/70 and CRT common receptor, CD91. The activation of DC by Bortezomib and AG 490 treated PEL cells, as seen in the present study, might have important implications for a combined chemo and immunotherapy in such patients.

Proteomic signatures of human oral epithelial cells in HIV-infected subjects

The oral epithelium, the most abundant structural tissue lining the oral mucosa, is an important line of defense against infectious microorganisms. HIV infected subjects on highly active antiretroviral therapy (HAART) are susceptible to comorbid viral, bacterial and fungal infections in the oral cavity. To provide an assessment of the molecular alterations of oral epithelia potentially associated with susceptibility to comorbid infections in such subjects, we performed various proteomic studies on over twenty HIV infected and healthy subjects. In a discovery phase two Dimensional Difference Gel Electrophoresis (2-D DIGE) analyses of human oral gingival epithelial cell (HOEC) lysates were carried out; this identified 61 differentially expressed proteins between HIV-infected on HAART subjects and healthy controls. Down regulated proteins in HIV-infected subjects include proteins associated with maintenance of protein folding and pro- and anti-inflammatory responses (e.g., heat-shock proteins, Cryab, Calr, IL-1RA, and Galectin-3-binding protein) as well as proteins involved in redox homeostasis and detoxification (e.g., Gstp1, Prdx1, and Ero1). Up regulated proteins include: protein disulfide isomerases, proteins whose expression is negatively regulated by Hsp90 (e.g., Ndrg1), and proteins that maintain cellular integrity (e.g., Vimentin). In a verification phase, proteins identified in the protein profiling experiments and those inferred from Ingenuity Pathway Analysis were analyzed using Western blotting analysis on separate HOEC lysate samples, confirming many of the discovery findings. Additionally in HIV-infected patient samples Heat Shock Factor 1 is down regulated, which explains the reduced heat shock responses, while activation of the MAPK signal transduction cascade is observed. Overall, HAART therapy provides an incomplete immune recovery of the oral epithelial cells of the oral cavity for HIV-infected subjects, and the toxic side effects of HAART and/or HIV chronicity silence expression of multiple proteins that in healthy subjects function to provide robust innate immune responses and combat cellular stress.

Overactivation of plasmacytoid dendritic cells inhibits antiviral T-cell responses: a model for HIV immunopathogenesis

A delicate balance between immunostimulatory and immunosuppressive signals mediated by dendritic cells (DCs) and other antigen-presenting cells (APCs) regulates the strength and efficacy of antiviral T-cell responses. HIV is a potent activator of plasmacytoid DCs (pDCs), and chronic pDC activation by HIV promotes the pathogenesis of AIDS. Cholesterol is pivotal in maintaining HIV envelope integrity and allowing HIV-cell interaction. By depleting envelope-associated cholesterol to different degrees, we generated virions with reduced ability to activate pDCs. We found that APC activation was dissociated from the induction of type I IFN-α/β and indoleamine-2,3-dioxygenase (IDO)-mediated immunosuppression in vitro. Extensive cholesterol withdrawal, resulting in partial protein and RNA loss from the virions, rendered HIV a more powerful recall immunogen for stimulating memory CD8 T-cell responses in HIV-exposed, uninfected individuals. These enhanced responses were dependent on the inability of cholesterol-depleted HIV to induce IFN-α/β.

Circulating heat shock protein 70 in health, aging and disease

Background

Heat shock proteins (Hsp) are ubiquitously synthesised in virtually all species and it is hypothesised that they might have beneficial health effects. Recent studies have identified circulating Hsp as an important mediator in inflammation - the effects of low-grade inflammation in the aging process are overwhelming. While much is known about intracellular Hsp70, scant data exist on circulating Hsp70 in the aging context. Therefore, the objectives of this study were to investigate the effect of age and disease on circulating Hsp70 and, in particular, to evaluate the association between circulating Hsp70 and inflammatory parameters.

Results

Serum Hsp70, Interleukin (IL) -10, IL-6 and Tumor Necrosis Factor (TNF) alpha concentrations were determined in 90 hospitalised geriatric patients (aged 83 ± 6 years) and in 200 community-dwelling control subjects (100 elderly, aged 74 ± 5 years, and 100 young, aged 23 ± 3 years). In the community-dwelling elderly, serum Hsp70 and IL-10 concentrations were significantly lower and IL-6 was significantly higher when compared to healthy young control subjects. Elderly patients presenting inflammation (CRP serum levels ≥5 mg/L) showed significantly (p = 0.007) higher Hsp70 values; and Hsp70 correlated positively (p < 0.001) with IL-6 and CRP, but not with TNF-alpha or IL-10. A significant association was also noted between Hsp70 levels and the degree of dependency and cognitive decline in geriatric patients.

Conclusions

The present data provide new evidence that serum concentration of Hsp70 decreases with age in a normal population. Our study also shows that higher levels of Hsp70 are associated with inflammation and frailty in elderly patients.

TLR activation pathways in HIV-1-exposed seronegative individuals

TLRs trigger innate immunity that recognizes conserved motifs of invading pathogens, resulting in cellular activation and release of inflammatory factors. The influence of TLR activation on resistance to HIV-1 infection has not been investigated in HIV-1 exposed seronegative (ESN) individuals. PBMCs isolated from heterosexually ESN individuals were stimulated with agonists specific for TLR3 (poly I:C), TLR4 (LPS), TLR7 (imiquimod), and TLR7/8 (ssRNA40). We evaluated expression of factors involved in TLR signaling cascades, production of downstream effector immune mediators, and TLR-expression in CD4+ and CD14+ cells. Results were compared with those obtained in healthy controls (HCs). ESN individuals showed: 1) comparable percentages of CD14+/TLR4+ and CD4+/TLR8+ CD14+/TLR8+ cells; 2) higher responsiveness to poly I:C, LPS, imiquimod, and ssRNA40 stimulation, associated with significantly increased production of IL-1beta, IL-6, TNF-alpha, and CCL3; 3) augmented expression of mRNA specific for other targets (CCL2, CSF3, CSF2, IL-1alpha, IL-8, IL-10, IL-12, cyclooxygenase 2) demonstrated by broader TLRs pathway expression analyses; and 4) increased MyD88/MyD88s(short) ratio, mainly following TLR7/8 stimulation. We also compared TLR-agonist-stimulated cytokine/chemokine production in CD14+ PBMCs and observed decreased IFN-beta production in ESN individuals compared with HCs upon TLR7/8-agonist stimulation. These data suggest that TLR stimulation in ESN individuals results in a more robust release of immunologic factors that can influence the induction of stronger adaptive antiviral immune responses and might represent a virus-exposure-induced innate immune protective phenotype against HIV-1.

Glycoprotein 96-mediated presentation of human immunodeficiency virus type 1 (HIV-1)-specific human leukocyte antigen class I-restricted peptide and humoral immune responses to HIV-1 p24

Viral antigens complexed to heat shock proteins (HSPs) can enhance antiviral immunity. The present study evaluated the immunogenicity of a novel human immunodeficiency virus type 1B' (HIV-1B')-specific, human leukocyte antigen A2 (HLA-A2)-restricted peptide (FLQSRPEPTA, Gag(448-457)) and the cellular immune adjuvant effect of HSP gp96 using the HLA-A2 transgenic mouse model. It was found that gp96 could augment cytotoxic-T-lymphocyte responses specific for the 10-mer peptide of HIV-1B'. This study also evaluated the humoral immune adjuvant effect of HSP gp96 and its N-terminal fragment (N336) and found that immunization of BALB/c mice with a mixture of gp96 or its N-terminal fragment and HIV-1 p24 antigen or with an p24-N336 fusion protein resulted in a significant increase in anti-HIV p24 antibody titer. These results demonstrate the possibility of using gp96 and its N fragment as adjuvants to augment cellular and humoral immune responses against HIV-1 infection.

Human plasmacytoid dendritic cells interact with gp96 via CD91 and regulate inflammatory responses

Glucose-regulated stress protein gp96 is known to be involved in the host response to pathogens and to cancer. Our study explored the relationships between gp96 and human blood plasmacytoid dendritic cells (pDC) and proved that gp96 directly targets pDC by a receptor-dependent interaction. Competition studies identified CD91 as a gp96 receptor on pDC, and laser confocal imaging indicated that CD91 triggering was followed by gp96 endocytosis and trafficking into early endosomes and later into the endoplasmic reticulum compartment. Using two alternative Abs, we showed that human blood pDC reproducibly expressed CD91, although different levels of expression were detectable among the analyzed donors. Moreover, CpG-matured pDC displayed CD91 receptor up-regulation that correlated with an increased gp96 binding. Functionally, gp96-pDC interaction activated the NF-kappaB pathway, leading to the nuclear translocation of the NF-kappaB complex. gp96-treated pDC maintained an immature phenotype, while they down-modulated the release of IL-8, suggesting an anti-inflammatory role of this pathway, and they strongly up-regulated the cell surface expression of the gp96 receptor CD91. CpG-matured or gp96-treated pDC, expressing high levels of the gp96 receptor CD91, antagonized the gp96-induced activation of monocyte-derived dendritic cells in terms of cell surface phenotype and cytokine production. Altogether, these results suggest that gp96-pDC interaction might represent an active mechanism controlling the strength of the immune response to free, extracellular available gp96; this mechanism could be particularly relevant in wounds and chronic inflammation.

Identification of differentially expressed proteins in the cervical mucosa of HIV-1-resistant sex workers

Novel tools are necessary to understand mechanisms of altered susceptibility to HIV-1 infection in women of the Pumwani Sex Worker cohort, Kenya. In this cohort, more than 140 of the 2000 participants have been characterized to be relatively resistant to HIV-1 infection. Given that sexual transmission of HIV-1 occurs through mucosal surfaces such as that in the cervicovaginal environment, our hypothesis is that innate immune factors in the genital tract may play a role in HIV-1 infection resistance. Understanding this mechanism may help develop microbicides and/or vaccines against HIV-1. A quantitative proteomics technique (2D-DIGE: two-dimensional difference in-gel electrophoresis) was used to examine cervical mucosa of HIV-1 resistant women ( n = 10) for biomarkers of HIV-1 resistance. Over 15 proteins were found to be differentially expressed between HIV-1-resistant women and control groups ( n = 29), some which show a greater than 8-fold change. HIV-1-resistant women overexpressed several antiproteases, including those from the serpin B family, and also cystatin A, a known anti-HIV-1 factor. Immunoblotting for a selection of the identified proteins confirmed the DIGE volume differences. Validation of these results on a larger sample of individuals will provide further evidence these biomarkers are associated with HIV-1 resistance and could help aid in the development of effective microbicides against HIV-1.

Immunological correlates of protection from HIV infection and disease

The recent meeting on "Immune Correlates of Protection from HIV Infection and Disease" examined new data from a variety of preclinical and clinical settings. These new insights may facilitate vaccine design and clinical evaluation.

Autologous renal cell cancer vaccines using heat shock protein-peptide complexes

Investigations into the role of heat shock proteins (HSPs) in immune response have progressed well into a third decade, and indications of their use for the treatment of renal cell carcinoma (RCC) in the adjuvant setting will be revealed in the near future when a randomized phase III clinical trial is completed. Additional ongoing and planned randomized clinical trials will test the efficacy of HSP-based vaccines in more advanced stages of RCC. This review describes the compelling scientific rationale behind testing HSPs in RCC against the backdrop of other immunotherapeutic approaches in this indication.

Dominant ex vivo cross-stimulation of CD8+ T-cells with whole soluble gag protein in HIV-infected subjects

BACKGROUND

Soluble HIV proteins are often used to detect HIV-specific CD4+ T-helper cell responses in vitro. However, exogenous antigens can also indirectly stimulate CD8+ T-cells and thus complicate assessment of CD4+ T-cell responses.

OBJECTIVE

To analyze the extent of in vitro HIV-1 Gag p55 protein cross-stimulation to CD8+ T-cells in therapy-naive and highly active antiretroviral therapy (HAART)-treated HIV patients and to correlate this phenomenon with HIV disease progression.

METHODS

Gag protein-stimulated T-cell responses were measured in total and CD8-depleted peripheral blood mononuclear cells (PBMCs) by interferon (IFN)-gamma enzyme-linked immunosorbent spot (ELISPOT) assays in 20 therapy-naive and 60 HAART-treated HIV patients. Numbers of spot forming cells (SFCs) relative to CD4+ and CD8+ T-cell subsets were calculated. Gag protein-stimulated responses were correlated with markers of disease progression.

RESULTS

Stimulation of PBMC with HIV-1 Gag protein induced higher CD8+ T-cell responses than CD4+ T-cell responses in both therapy-naive and HAART-treated HIV patients (P < 0.001). Gag protein cross-stimulation of CD8+ T-cells was higher in therapy-naive than in HAART-treated HIV patients (P < 0.001). In HAART-treated HIV patients, we detected an inverse correlation between Gag protein cross-stimulation of CD8+ T-cells and the CD4 count (R = -0.311; P = 0.016). Depletion of CD14+ cells abrogated the responses, suggesting that Gag protein cross-stimulation of CD8+ T-cells depends on antigen processing and presentation by antigen-presenting cells (APCs).

CONCLUSIONS

HIV protein cross-presentation to CD8+ T-cells should be taken into account when detecting HIV-specific T-cell responses by stimulation of PBMCs with whole exogenous antigens.