Disease-associated dendritic cells respond to disease-specific antigens through the common heat shock protein receptor

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.

Cells of the Innate and Adaptive Immune Systems in Kaposi's Sarcoma

Kaposi's sarcoma (KS) is an angioproliferative malignancy whose associated etiologic agent is the Kaposi's sarcoma-associated herpesvirus (KSHV). KS is the most prevalent malignancy among HIV-infected individuals globally and is considered an AIDS-defining malignancy. The different forms of KS including HIV-associated KS, iatrogenic (immunosuppression-related) KS, and classical KS in elderly males suggest that immune cell dysregulation is among the key components in promoting KS development in KSHV-infected individuals. It is therefore expected that different cell types of the immune system likely play distinct roles in promoting or inhibiting KS development. This narrative review is focused on discussing cells of the innate and adaptive immune systems in KSHV infection and KS pathogenesis, including how these cells can be useful in the control of KSHV infection and treatment of KS.

Antibodies to Heat Shock Proteins 90α and 90β in Psoriasis

One of many hypotheses of psoriasis pathogenesis supposes an overexpression of heat shock proteins (Hsps) in different skin layers and systemic immunologic response to them. Hsp90 is one of the most abundant chaperone in eukaryotic cells. The number of studies concerning the role of Hsp90 and anti-Hsp90 antibodies in etiopathogenesis of various diseases is also constantly expanding. Still, there are not many reports concerning potential involvement of this Hsp family or anti-Hsp90 immunization in pathomechanism of psoriasis. The aim of the study was the estimation of anti-Hsp90α and anti-Hsp90β IgG antibodies in the sera of the psoriatic patients at different phases of disease activity in comparison to the sera of healthy individuals. The study material consisted of sera from psoriasis patients (n = 80) in active phase and in the remission phase and healthy individuals (n = 80). Concentrations of anti-Hsp90α and anti-Hsp90β IgG antibodies were determined using ELISA technique. In the patients with psoriasis (both in the active phase of the disease and in the remission phase) concentrations of anti-Hsp90α antibodies were significantly higher than in healthy individuals and they correlated positively with psoriasis area severity index values. The mean concentrations of anti-Hsp90β antibodies in the psoriatic patients and healthy controls were comparable. The obtained results indicate an existence of increased immunological response to Hsp90α in psoriasis. It may suggest the role of the extracellular form of this chaperone and/or anti-Hsp90α antibodies in etiopathogenesis of this dermatosis. The inhibition of Hsp90α may represent a novel therapeutic approach to treat psoriasis.

Distribution of Dendritic Cells in AIDS-Associated Oral Kaposi's Sarcoma

The aim of this study was to determine if the distribution of Langerhans cells (LC) and interstitial dendritic cells (IDC) is altered in AIDS-associated oral Kaposi's sarcoma when compared to HIV-negative highly vascular oral lesions. Fifty-one cases of AIDS-associated oral Kaposi's sarcoma and 20 of highly vascular oral lesions were retrospectively retrieved. All cases of Kaposi's sarcoma were confirmed with immunoreactions against CD34 and HHV-8. Clinical data regarding sex, age and lesions location were obtained from pathology reports. Immunohistochemistry against CD207 (immature dendritic cells) and CD83 (mature dendritic cells) were done. LC were in the epithelium and IDC in the stroma. CD207+ cells predominated in the epithelium of the lesions, whereas CD83+ cells predominated in their stromal compartment. Kaposi's sarcoma had a lower CD207+ immature LC count (p=0.02) and an increased CD207+ IDC than highly vascular oral lesions (p<0.001). Moreover, Kaposi's sarcoma also showed an increased number of mature CD83+ IDC than highly vascular oral lesions (p<0.001). There were significant alterations in the distribution of LC and IDC in AIDS-associated Kaposi's sarcoma when compared to HIV-negative vascular oral lesions, suggesting that changes in their concentrations may play a role in the pathogenesis of Kaposi's sarcoma.

Interference with the Autophagic Process as a Viral Strategy to Escape from the Immune Control: Lesson from Gamma Herpesviruses

We summarized the most recent findings on the role of autophagy in antiviral immune response. We described how viruses have developed strategies to subvert the autophagic process. A particular attention has been given to Epstein-Barr and Kaposi's sarcoma associated Herpesvirus, viruses studied for many years in our laboratory. These two viruses belong to γ-Herpesvirus subfamily and are associated with several human cancers. Besides the effects on the immune response, we have described how autophagy subversion by viruses may also concur to the enhancement of their replication and to viral tumorigenesis.

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.

Dendritic cells: key players in human herpesvirus 8 infection and pathogenesis

Human herpesvirus 8 (HHV-8; Kaposi's sarcoma-associated herpesvirus) is an oncogenic gammaherpesvirus that primarily infects cells of the immune and vascular systems. HHV-8 interacts with and targets professional antigen presenting cells and influences their function. Infection alters the maturation, antigen presentation, and immune activation capabilities of certain dendritic cells (DC) despite non-robust lytic replication in these cells. DC sustains a low level of antiviral functionality during HHV-8 infection in vitro. This may explain the ability of healthy individuals to effectively control this virus without disease. Following an immune compromising event, such as organ transplantation or human immunodeficiency virus type 1 infection, a reduced cellular antiviral response against HHV-8 compounded with skewed DC cytokine production and antigen presentation likely contributes to the development of HHV-8 associated diseases, i.e., Kaposi's sarcoma and certain B cell lymphomas. In this review we focus on the role of DC in the establishment of HHV-8 primary and latent infection, the functional state of DC during HHV-8 infection, and the current understanding of the factors influencing virus-DC interactions in the context of HHV-8-associated disease.

Immune escape of γ-herpesviruses from adaptive immunity

Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV) are two γ-herpesviruses identified in humans and are strongly associated with the development of malignancies. Murine γ-herpesvirus (MHV-68) is a naturally occurring rodent pathogen, representing a unique experimental model for dissecting γ-herpesvirus infection and the immune response. These γ-herpesviruses actively antagonize the innate and adaptive antiviral responses, thereby efficiently establishing latent or persistent infections and even promoting development of malignancies. In this review, we summarize immune evasion strategies of γ-herpesviruses. These include suppression of MHC-I-restricted and MHC-II-restricted antigen presentation, impairment of dendritic cell functions, downregulation of costimulatory molecules, activation of virus-specific regulatory T cells, and induction of inhibitory cytokines. There is a focus on how both γ-herpesvirus-derived and host-derived immunomodulators interfere with adaptive antiviral immunity. Understanding immune-evasive mechanisms is essential for developing future immunotherapies against EBV-driven and KSHV-driven tumors.

STAT3 activation by KSHV correlates with IL-10, IL-6 and IL-23 release and an autophagic block in dendritic cells

Kaposis's sarcoma associated herpesvirus (KSHV) has been reported to infect, among others, monocytes and dendritic cells DCs impairing their function. However, the underlying mechanisms remain not completely elucidated yet. Here we show that DC exposure to active or UV-inactivated KSHV resulted in STAT3 phosphorylation. This effect, partially dependent on KSHV-engagement of DC-SIGN, induced a high release of IL-10, IL-6 and IL-23, cytokines that in turn might maintain STAT3 in a phosphorylated state. STAT3 activation also correlated with a block of autophagy in DCs, as indicated by LC3II reduction and p62 accumulation. The IL-10, IL-6 and IL-23 release and the autophagic block could be overcome by inhibiting STAT3 activation, highlighting the role of STAT3 in mediating such effects. In conclusion, here we show that STAT3 activation can be one of the molecular mechanisms leading to KSHV-mediated DC dysfunction, that might allow viral persistence and the onset of KSHV-associated malignancies.

Reduced expression of members of the mhc-i antigen processing machinery in ethnic Uighur women with cervical cancer in the Xinjiang region of China

OBJECTIVE

Cervical cancer is a major cause of mortality in Uighur women compared with Han women in the Xinjiang region of China. Although a reduction in the class i major histocompatibility complex (mhc-i) antigen processing machinery (apm) is associated with the development of cervical cancer, the mhc-i apm has not been studied in this particular group of women, who have the highest incidence rate of cervical cancer in China.

STUDY DESIGN

We used immunohistochemical staining and polymerase chain reaction amplification of viral dna from infection with the human papilloma virus (hpv) to study the expression of members of the mhc-i apm in cervical cancer sections collected from Uighur and Han women and in cervicitis samples from age-matched counterparts.

RESULTS

Expression of the molecules of interest was compared between two ethnic groups, and expression of transporter associated with antigen processing 1 and 2, heat shock protein 90, and calnexin were found to be reduced even more significantly in Han women with cervical cancer than in Uighur women with same disease. However, compared with Han women, Uighur women had a higher rate of infection with hpv 16.

CONCLUSIONS

The mhc-i apm were reduced in cervical cancer, with heterogeneity in the two ethnic groups. The reduction was more pronounced in Han women, who less frequently had hpv 16 infection, suggesting possible differences in the roles of members of the mhc-i apm and in the mechanisms of cervical cancer development in these two ethnic groups despite residence in the same region of China.

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.

Heat Shock Protein Vaccines: From Bench to Bedside

Heat shock proteins (HSPs) are immunogenic, with the specificity of the immune response provided by the peptides that they chaperone. Binding of cell surface receptors by HSPs is central to the elicitation of the innate and adaptive immune responses obtained after vaccination and also plays a physiologic role in cross-priming. These effects of HSPs have been exploited in prophylaxis and therapy of cancer and infectious disease. The data obtained from murine studies have been translated into ongoing clinical trials of cancer of which the most recent results are provided here.

Heat Shock Proteins and Scavenger Receptors: Role in Adaptive Immune Responses

Tumor-derived heat shock proteins have shown promise as anti-cancer vaccines in clinical trials. Heat shock proteins (HSPs) can generate potent anti-tumor immunity and elicit antigen-specific CD8+ T cell responses in murine studies. Antigen presenting cells (APC), such as macrophages and dendritic cells (DCs), can elicit antigen-specific CD8+ T cell responses mediated by HSPs. CD91 was the first identified endocytic scavenger receptor for HSPs on APC that can facilitate the process of cross-presentation. Other scavenger receptors may also play a similar role in this process. The present review critically evaluates the identified HSP endocytic receptors on APCs that may generate adaptive immune responses. A better understanding of this interaction between HSPs and APCs may further unravel mechanisms of immunoadjuvant function of HSPs.

Murine gammaherpesvirus-68 productively infects immature dendritic cells and blocks maturation

Many viruses have evolved mechanisms to evade host immunity by subverting the function of dendritic cells (DCs). This study determined whether murine gammaherpesvirus-68 (gamma HV-68) could infect immature or mature bone-marrow-derived DCs and what effect infection had on DC maturation. It was found that gamma HV-68 productively infected immature DCs, as evidenced by increased viral titres over time. If DCs were induced to mature by exposure to LPS and then infected with gamma HV-68, only a small percentage of cells was productively infected. However, limiting-dilution assays to measure viral reactivation demonstrated that the mature DCs were latently infected with gamma HV-68. Electron microscopy revealed the presence of capsids in the nucleus of immature DCs but not in mature DCs. Interestingly, infection of immature DCs by gamma HV-68 did not result in upregulation of the co-stimulatory molecules CD80 and CD86 or MHC class I and II, or induce cell migration, suggesting that the virus infection did not induce DC maturation. Furthermore, gamma HV-68 infection of immature DCs did not result in elevated interleukin-12, an important cytokine in the induction of T-cell responses. Finally, lipopolysaccharide and poly(I : C) stimulation of gamma HV-68-infected immature DCs did not induce increases in the expression of co-stimulatory molecules and MHC class I or II compared with mock-treated cells, suggesting that gamma HV-68 infection blocked maturation. Taken together, these data demonstrate that gamma HV-68 infection of DCs differs depending on the maturation state of the DC. Moreover, the block in DC maturation suggests a possible immunoevasion strategy by gamma HV-68.

Prognostic Significance of Immune Subset Measurement in Individuals With AIDS-Associated Kaposi's Sarcoma

Purpose

A prognostic index for AIDS-associated Kaposi's sarcoma (KS) diagnosed in the era of highly active antiretroviral therapy (HAART) was based on routine clinical and laboratory characteristics. Because immune subset measurement is often performed in HIV-positive individuals, we examined whether these were predictive of mortality independently of the prognostic index, or could predict time to progression of KS.

Patients and Methods

We performed univariate and multivariate Cox regression analyses on a data set of 326 individuals with AIDS-associated KS to identify immune subset covariates predictive of overall survival and time to progression. Adaptive (CD8 T cell and CD19 B cell) and innate (CD16/56 natural-killer cell) immune parameters were studied by flow cytometry.

Results

In univariate analyses, all three immune subsets had significant effects on overall survival (P < .025). In multivariate analyses including the prognostic index, only CD8 counts remained significant (P = .026), although its effect on the overall prognostic index is small. An increase of 100 cells/mm3 in the CD8 count confers a 5% improvement in overall survival. Individuals with a higher CD8 count did not have an increased time to progression. Patients who were already on HAART at the time of KS diagnosis did not have a shorter time to progression than those who were antiretroviral naïve at KS diagnosis.

Conclusion

The CD8 count appears to provide independent prognostic information in individuals with AIDS-associated KS. Measurement of the CD8 count is clinically useful in patients with KS.

VWF protects FVIII from endocytosis by dendritic cells and subsequent presentation to immune effectors

Von Willebrand factor (VWF) is a chaperone molecule for procoagulant factor VIII (FVIII). Its role in the reduction of the immunogenicity of therapeutic FVIII in patients with hemophilia A has been evoked but lacks clear cellular and molecular rationale. Here, we demonstrate that VWF protects FVIII from being endocytosed by human dendritic cells (DCs) and subsequently presented to FVIII-specific T cells. The immunoprotective effect of VWF requires a physical interaction with FVIII because the endocytosis of FVIII was significantly restored on hindering the formation of the VWF-FVIII complex. Interestingly, VWF had no direct inhibitory effect either on the ability of DCs to present antigenic peptides or on the activation potency of CD4+ T cells. We thus propose that VWF may reduce the immunogenicity of FVIII by preventing, upstream from the activation of immune effectors, the entry of FVIII in professional antigen-presenting cells.

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.

Quantitative and functional defects of dendritic cells in classic Kaposi's sarcoma

In this study, we investigated whether dendritic cells (DCs) are altered in classic Kaposi's sarcoma (cKS), a lympho-angioproliferative disorder associated with human herpesvirus-8 (HHV-8) infection. By direct analysis of peripheral blood DCs (PBDCs), we demonstrated that cKS patients have lower frequency of myeloid and plasmacytoid DCs than controls. This reduction was greater in patients with advanced stages of disease. PBDCs from cKS patients also showed up-regulated expression of the scavenger receptor CD91 and impaired IL-12 expression. PB monocytes that represent DC precursors in vivo and in vitro showed the same alterations; accordingly, DCs differentiated in vitro from cKS monocytes were similarly affected. The same alterations were induced by addition of cKS plasma during DC differentiation from control monocytes. These results indicate that PBDCs and their precursors are altered in cKS and suggest that soluble circulating factors participate in this process. The study may provide new insights into the pathogenesis of cKS.

Immunotherapy for human cancer using heat shock protein-peptide complexes

Heat shock proteins (HSPs) are primordial and abundant molecules expressed in all cells. Publications starting in 1984 have shown that immunization of mice, rats, and frogs with purified preparations of selected HSPs isolated from cancers leads to protective immunity against the cancer used as the source of the HSP. The basis of the tumor-specific immunogenicity of these molecules lies not in the molecules themselves but in the array of peptides, including antigenic peptides chaperoned by them. These experiments and the ideas derived from them form the basis of an approach to immunotherapy for human cancer that began in 1995 and is now in full swing.

A novel method to identify and characterise peptide mimotopes of heat shock protein 70-associated antigens

The heat shock protein, Hsp70, has been shown to play an important role in tumour immunity. Vaccination with Hsp70-peptide complexes (Hsp70-PCs), isolated from autologous tumour cells, can induce protective immune responses. We have developed a novel method to identify synthetic mimic peptides of Hsp70-PCs and to test their ability to activate T-cells. Peptides (referred to as "recognisers") that bind to Hsp70-PCs from the human breast carcinoma cell line, MDA-MB-231, were identified by bio-panning a random peptide M13 phage display library. Synthetic recogniser peptides were subsequently used as bait in a reverse bio-panning experiment to identify potential Hsp70-PC mimic peptides. The ability of the recogniser and mimic peptides to prime human lymphocyte responses against tumour cell antigens was tested by stimulating lymphocytes with autologous peptide-loaded monocyte-derived dendritic cells (DCs). Priming and subsequent stimulation with either the recogniser or mimic peptide resulted in interferon-gamma (IFN-gamma) secretion by the lymphocytes. Furthermore, DCs loaded with Hsp70, Hsp70-PC or the recogniser or the mimic peptide primed the lymphocytes to respond to soluble extracts from breast cells. These results highlight the potential application of synthetic peptide-mimics of Hsp70-PCs, as modulators of the immune response against tumours.

The presentation and survival of patients with non-cutaneous AIDS-associated Kaposi's sarcoma

BACKGROUND

Acquired immune deficiency syndrome related Kaposi's sarcoma (AIDS-KS) remains a significant cause of morbidity and mortality. We describe for the first time a proportion of patients with AIDS-KS who presented with no evidence of cutaneous disease.

PATIENTS AND METHODS

From our cohort of 5932 individuals infected with the human immunodeficiency virus (HIV-1) treated in the HAART era, 319 were identified with KS. Of these, 11 patients (5.4%) were diagnosed with KS without the presence of any cutaneous disease. We compared their survival, clinical, immunological and virological characteristics to other individuals with KS.

RESULTS

There were no statistically significant differences in survival, CD4 count or HIV viral load at KS presentation. We observed that tumour-associated oedema (P = 0.046) and non-oral gastrointestinal KS (P = 0.042) were significantly more common in patients with non-cutaneous KS. Only one case of non-cutaneous KS was observed prior to the era of highly active anti-retroviral therapy (HAART).

CONCLUSIONS

Non-cutaneous KS is a recognisable condition; patients should be treated with the standard of care as their prognosis is not inferior. This is likely to reflect a strong immune response, in the era of HAART.

Infection of dendritic cells by a gamma2-herpesvirus induces functional modulation

The murine gamma-herpesvirus-68 (gammaHV68) establishes viral latency in dendritic cells (DCs). In the present study, we examined the specific consequences of DC infection by gammaHV68, both in vivo and in vitro. Ex vivo analysis of infected mice showed that the virus colonizes respiratory DCs very early after infection and that all subsets of splenic DCs analyzed are viral targets. We have developed and characterized an in vitro model of gammaHV68 infection of DCs. Using this model, we demonstrated that viral infection neither induces full DC maturation nor interferes with exogenous activation, which is assessed by cell surface phenotypic changes. However, whereas gammaHV68 infection alone failed to elicit cytokine secretion, IL-10 secretion of exogenously activated DCs was enhanced. Furthermore, gammaHV68-infected DCs efficiently stimulated virus-specific T cell hybridomas but failed to induce alloreactive stimulation of normal T cells. These data indicate that viral infection doesn't interfere with Ag processing and presentation but does interfere with the ability of DCs to activate T cells. The inhibition of T cell activation was partially reversed by blocking IL-10. Analysis of infected mice shows elevated levels of IL-10 expression in DCs and that lack of endogenous IL-10 is associated with decreased gammaHV68 long-term latency. Taken together, these observations indicate that gamma2-herpesvirus infection of DCs is a mechanism of viral immune evasion, partially mediated by IL-10.

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

The significantly higher surface expression of the surface heat-shock protein receptor CD91 on monocytes of human immunodeficiency virus type-1 (HIV-1)-infected, long-term nonprogressors suggests that HIV-1 antigen uptake and cross-presentation mediated by CD91 may contribute to host anti-HIV-1 defenses and play a role in protection against HIV-1 infection. To investigate this further, we performed phenotypic analysis to compare CD91 surface expression on CD14(+) monocytes derived from a cohort of HIV-1-exposed seronegative (ESN) subjects, their seropositive (SP) partners, and healthy HIV-1-unexposed seronegative (USN) subjects. The median fluorescent intensity (MFI) of CD91 on CD14(+) monocytes was significantly higher in ESN compared with SP (P = 0.028) or USN (P = 0.007), as well as in SP compared with USN subjects (P = 0.018). CD91 MFI was not normalized in SP subjects on highly active antiretroviral therapy (HAART) despite sustainable, undetectable plasma viraemia. Data in three SP subjects experiencing viral rebounds following interruption of HAART showed low CD91 MFI comparable with levels in USN subjects. There was a significant positive correlation between CD91 MFI and CD8(+) T cell counts in HAART-naïve SP subjects (r = 0.7, P = 0.015). Increased surface expression of CD91 on CD14(+) monocytes is associated with the apparent HIV-1 resistance that is observed in ESN subjects.

Activation of dendritic antigen-presenting cells expressing common heat shock protein receptor CD91 during induction of psoriasis

BACKGROUND

Psoriasis is a common and chronic relapsing inflammatory skin disorder. Although a role for T cells in mediating the induction and maintenance of psoriatic lesions is well established, mechanisms responsible for activation of T cells by antigen-presenting cells (APCs) during disease relapse are poorly understood.

OBJECTIVES

(i) To determine whether expression of the common heat shock protein (HSP) receptor CD91 correlated with development of psoriasis in a mouse model of psoriasis, (ii) to characterize the lesional cells on which CD91 was expressed, and (iii) to investigate whether CD91+ cells in psoriasis showed signs of activation.

METHODS

Two systems were used in order to study the above-mentioned objectives: (i) skin biopsies taken directly from patients with psoriasis (either psoriatic plaques or symptomless prepsoriatic skin) or from healthy donors, respectively, or (ii) (human) skin biopsies collected during development of psoriasis using a novel xenograft mouse model of psoriasis. The skin samples were then either processed for analysis by light microscopy, or labelled with fluorochrome-conjugated antibodies and analysed by confocal laser scanning microscopy.

RESULTS

We observed a markedly increased number of CD91+ cells which paralleled development of new psoriatic lesions in the psoriasis mouse model and in established psoriatic plaques compared with symptomless prepsoriatic or healthy skin. Morphology as well as cell-specific markers showed that CD91 was predominantly expressed by dermal dendritic APCs characterized by activation of nuclear factor-kappaB signalling and the presence of tumour necrosis factor-alpha, an important proinflammatory cytokine in the immunopathogenesis of psoriasis. In addition, HSP70, a ligand for CD91, was increased in keratinocytes in close vicinity to CD91-bearing APCs in psoriatic lesions.

CONCLUSIONS

These findings indicate massive presence of CD91+ dendritic cells juxtaposed to lesional keratinocytes expressing HSP70, and suggest a novel pathophysiological pathway and therapeutic target for this chronic inflammatory skin disease.

The heat-shock protein receptors: some answers and more questions

The existence of heat-shock protein (HSP) receptors on antigen-presenting cells (APCs) was hypothesized in 1994. The first such receptor, CD91 or LRP, was identified and characterized in 2000. The pace of attribution has quickened since and during the last three years alone, six putative HSP receptors have been identified. These include CD40, LOX-1, CD36, Toll-like receptor-2 (TLR-2), TLR-4 and SR-A. The literature on HSP receptors on APCs is critically examined in this review and future directions are imagined.

The common heat shock protein receptor CD91 is up-regulated on monocytes of advanced melanoma slow progressors

Despite advances in our understanding of tumour immunology there is no therapy of proven survival benefit for advanced melanoma. Nevertheless, disease progression is slow in a small proportion of patients with metastatic melanoma, suggesting a contribution to outcome from host factors. Recent data have indicated the importance of the heat shock protein receptor CD91 in immune responses to, and progression of, infectious disease. Here we investigate the relationship between CD91 expression and outcome in malignancy. Rare melanoma patients were recruited with advanced disease that was progressing unusually slowly. CD91 expression on their monocytes was compared with control patients with more typical rapidly advancing metastatic disease. Th1 and Th2 cytokines, as well as innate and adaptive immune subsets, were also measured in the two groups. A significant increase in median CD91 expression levels was observed in slow progressors (P = 0.006). There were no differences in other immune subset markers or inflammatory cytokines. The ability of CD91 to internalize and cross-present tumour antigens through the major histocompatibility complex class I pathway may maintain CD8-positive cytotoxic T cell responses and contribute to slow progression of advanced melanoma.

Essential role of CD91 in re-presentation of gp96-chaperoned peptides

Heat shock proteins (HSPs) such as gp96 are released from cells as a result of necrotic cell death. The ability of endogenous HSP-peptide complexes to elicit antigen-specific T cells requires representation of the chaperoned peptides by antigen-presenting cells. Re-presentation requires the uptake of HSP-peptide complexes through a receptor, suggested to be the low-density lipoprotein receptor-related protein or CD91. We have used short interfering RNA for CD91 to show that, as antigen-presenting cells lose expression of CD91, their re-presenting ability undergoes a corresponding and dramatic decline. Furthermore, as the cells recover from extinction of CD91 expression, they regain the ability to re-present peptides. The ability of cells to bind alpha(2) macroglobulin, a previously known CD91 ligand, or HSP gp96, and their ability to process peptides chaperoned by alpha(2) macroglobulin, undergo identical variations. These results have been obtained from studies in vitro and from an assay that measures re-presentation in vivo. In additional studies in vivo, protective tumor immunity elicited by tumor-derived gp96-peptide complexes is shown to be abrogated by anti-CD91 antisera. These studies show that CD91 is essential for re-presentation of gp96-chaperoned peptides by MHC molecules and have an important bearing on the mechanism of immunogenicity of necrotic cells.

Kaposi's sarcoma as a model for cancer immunotherapy

Physicians have, for over a century, attempted to harness the potential therapeutic power of the immune system to treat patients with cancer. The discovery that cancer regression can be achieved by immune rejection of tumour antigens theoretically allows the eradication of neoplastic cells without toxicity to normal tissues. An understanding of the mode of presentation of tumour antigens, including those complexed to heat shock proteins by major histocompatibility complex (MHC) class I and class II molecules, and their recognition by CD8(+) and CD4(+) T cells, respectively, has further delineated the potential cancer rejection pathways involved. This also enables the sustained induction and expansion of specific anti-tumour T cells with cytolytic activity.