Serum HLA class I antigens: markers and modulators of an immune response?

Acute Myeloid Leukemia Causes Serious and Partially Irreversible Changes in Secretomes of Bone Marrow Multipotent Mesenchymal Stromal Cells

In patients with acute myeloid leukemia (AML), malignant cells modify the properties of multipotent mesenchymal stromal cells (MSCs), reducing their ability to maintain normal hematopoiesis. The aim of this work was to elucidate the role of MSCs in supporting leukemia cells and the restoration of normal hematopoiesis by analyzing ex vivo MSC secretomes at the onset of AML and in remission. The study included MSCs obtained from the bone marrow of 13 AML patients and 21 healthy donors. The analysis of proteins contained in the MSCs-conditioned medium demonstrated that secretomes of patient MSCs differed little between the onset of AML and remission; pronounced differences were observed between MSC secretomes of AML patients and healthy donors. The onset of AML was accompanied by a decrease in the secretion of proteins related to ossification, transport, and immune response. In remission, but not at the onset, secretion of proteins responsible for cell adhesion, immune response, and complement was reduced compared to donors. We conclude that AML causes crucial and, to a large extent, irreversible changes in the secretome of bone marrow MSCs ex vivo. In remission, functions of MSCs remain impaired despite the absence of tumor cells and the formation of benign hematopoietic cells.

Soluble HLA peptidome: A new resource for cancer biomarkers

Using circulating molecular biomarkers to screen for cancer and other debilitating disorders in a high-throughput and low-cost fashion is becoming increasingly attractive in medicine. One major limitation of investigating protein biomarkers in body fluids is that only one-fourth of the entire proteome can be routinely detected in these fluids. In contrast, Human Leukocyte Antigen (HLA) presents peptides from the entire proteome on the cell surface. While peptide-HLA complexes are predominantly membrane-bound, a fraction of HLA molecules is released into body fluids which is referred to as soluble HLAs (sHLAs). As such peptides bound by sHLA molecules represent the entire proteome of their cells/tissues of origin and more importantly, recent advances in mass spectrometry-based technologies have allowed for accurate determination of these peptides. In this perspective, we discuss the current understanding of sHLA-peptide complexes in the context of cancer, and their potential as a novel, relatively untapped repertoire for cancer biomarkers. We also review the currently available tools to detect and quantify these circulating biomarkers, and we discuss the challenges and future perspectives of implementing sHLA biomarkers in a clinical setting.

The Impact of Inflammation on the Immune Responses to Transplantation: Tolerance or Rejection?

Transplantation (Tx) remains the optimal therapy for end-stage disease (ESD) of various solid organs. Although alloimmune events remain the leading cause of long-term allograft loss, many patients develop innate and adaptive immune responses leading to graft tolerance. The focus of this review is to provide an overview of selected aspects of the effects of inflammation on this delicate balance following solid organ transplantation. Initially, we discuss the inflammatory mediators detectable in an ESD patient. Then, the specific inflammatory mediators found post-Tx are elucidated. We examine the reciprocal relationship between donor-derived passenger leukocytes (PLs) and those of the recipient, with additional emphasis on extracellular vesicles, specifically exosomes, and we examine their role in determining the balance between tolerance and rejection. The concept of recipient antigen-presenting cell "cross-dressing" by donor exosomes is detailed. Immunological consequences of the changes undergone by cell surface antigens, including HLA molecules in donor and host immune cells activated by proinflammatory cytokines, are examined. Inflammation-mediated donor endothelial cell (EC) activation is discussed along with the effect of donor-recipient EC chimerism. Finally, as an example of a specific inflammatory mediator, a detailed analysis is provided on the dynamic role of Interleukin-6 (IL-6) and its receptor post-Tx, especially given the potential for therapeutic interdiction of this axis with monoclonal antibodies. We aim to provide a holistic as well as a reductionist perspective of the inflammation-impacted immune events that precede and follow Tx. The objective is to differentiate tolerogenic inflammation from that enhancing rejection, for potential therapeutic modifications. (Words 247).

Critical Review of Existing MHC I Immunopeptidome Isolation Methods

Major histocompatibility complex class I (MHC I) plays a crucial role in the development of adaptive immune response in vertebrates. MHC molecules are cell surface protein complexes loaded with short peptides and recognized by the T-cell receptors (TCR). Peptides associated with MHC are named immunopeptidome. The MHC I immunopeptidome is produced by the proteasome degradation of intracellular proteins. The knowledge of the immunopeptidome repertoire facilitates the creation of personalized antitumor or antiviral vaccines. A huge number of publications on the immunopeptidome diversity of different human and mouse biological samples-plasma, peripheral blood mononuclear cells (PBMCs), and solid tissues, including tumors-appeared in the scientific journals in the last decade. Significant immunopeptidome identification efficiency was achieved by advances in technology: the immunoprecipitation of MHC and mass spectrometry-based approaches. Researchers optimized common strategies to isolate MHC-associated peptides for individual tasks. They published many protocols with differences in the amount and type of biological sample, amount of antibodies, type and amount of insoluble support, methods of post-fractionation and purification, and approaches to LC-MS/MS identification of immunopeptidome. These parameters have a large impact on the final repertoire of isolated immunopeptidome. In this review, we summarize and compare immunopeptidome isolation techniques with an emphasis on the results obtained.

Identification of Tumor Antigens Among the HLA Peptidomes of Glioblastoma Tumors and Plasma

Glioblastoma multiforme (GBM) is the most aggressive brain tumor with poor prognosis to most patients. Immunotherapy of GBM is a potentially beneficial treatment option, whose optimal implementation may depend on familiarity with tumor specific antigens, presented as HLA peptides by the GBM cells. Further, early detection of GBM, such as by a routine blood test, may improve survival, even with the current treatment modalities. This study includes large-scale analyses of the HLA peptidome (immunopeptidome) of the plasma-soluble HLA molecules (sHLA) of 142 plasma samples, and the membranal HLA of GBM tumors of 10 of these patients' tumor samples. Tumor samples were fresh-frozen immediately after surgery and the plasma samples were collected before, and at multiple visits after surgery. In total, this HLA peptidome analysis involved 52 different HLA allotypes and resulted in the identification of more than 35,000 different HLA peptides. Strong correlations were observed in the signal intensities and in the repertoires of identified peptides between the tumors and plasma-soluble HLA peptidomes of the individual patients, whereas low correlations were observed between these HLA peptidomes and the tumors' proteomes. HLA peptides derived from Cancer/Testis Antigens (CTAs) were selected based on their presence among the HLA peptidomes of the patients and absence of expression of their source genes from any healthy and essential human tissues, except from immune-privileged sites. Additionally, peptides were selected as potential biomarkers if their levels in the plasma-sHLA peptidome were significantly reduced after the removal of tumor mass. The CTAs identified among the analyzed HLA peptidomes provide new opportunities for personalized immunotherapy and for early diagnosis of GBM.

Soluble HLA-I and HLA-II Molecules Are Potential Prognostic Markers of Progression of Systemic and Local Inflammation in Patients with COPD

Soluble molecules of the major histocompatibility complex play an important role in the development of various immune-mediated diseases. However, there is not much information on the participation of these proteins in the pathogenesis of chronic obstructive pulmonary disease (COPD). The aim of our work was to determine the content of soluble molecules of the major histocompatibility complex of classes I and II (sHLA-I and sHLA-II) in the exhaled breath condensate (EBC) and in the blood serum in patients with moderate to severe COPD during the exacerbation and stable phase. We investigated 105 patients (male) with COPD aged 46-67 and 21 healthy nonsmoking volunteers (male) comparable in age. The content of sHLA-I and sHLA-II molecules was studied using ELISA. We found an increase in the level of sHLA-I and sHLA-II molecules in EBC, as well as an enhancement in the serum content of sHLA-II in all the examined COPD patients compared to healthy nonsmoking volunteers. The revealed negative correlation between the serum concentration of sHLA-II and values of FEV1 and FEV1/FVC in all examined patients with COPD gives a possibility to consider the content of these proteins as an additional systemic marker of disease severity. The maximum endobronchial and serum concentrations of sHLA-I and sHLA-II were detected in patients with severe COPD during the exacerbation. The negative associations between the content of these molecules in EBC and serum and the parameters of lung function in patients with severe COPD were established. These findings suggest a pathogenetic role of sHLA-I and sHLA-II molecules in the mechanisms of the development and progression of local and systemic inflammation in COPD.

Identification of Tumor Antigens Among the HLA Peptidomes of Glioblastoma Tumors and Plasma

Glioblastoma multiforme (GBM) is the most aggressive brain tumor with poor prognosis to most patients. Immunotherapy of GBM is a potentially beneficial treatment option, whose optimal implementation may depend on familiarity with tumor specific antigens, presented as HLA peptides by the GBM cells. Furthermore, early detection of GBM, such as by a routine blood test, may improve survival, even with the current treatment modalities. This study includes large-scale analyses of the HLA peptidome (immunopeptidome) of the plasma-soluble HLA molecules (sHLA) of 142 plasma samples, and the membranal HLA of GBM tumors of 10 of these patients' tumor samples. Tumor samples were fresh-frozen immediately after surgery and the plasma samples were collected before, and at multiple visits after surgery. In total, this HLA peptidome analysis involved 52 different HLA allotypes and resulted in the identification of more than 35,000 different HLA peptides. Strong correlations were observed in the signal intensities and in the repertoires of identified peptides between the tumors and plasma-soluble HLA peptidomes of the individual patients, whereas low correlations were observed between these HLA peptidomes and the tumors' proteomes. HLA peptides derived from Cancer/Testis Antigens (CTAs) were selected based on their presence among the HLA peptidomes of the patients and absence of expression of their source genes from any healthy and essential human tissues, except from immune-privileged sites. Additionally, peptides were selected as potential biomarkers if their levels in the plasma-sHLA peptidome were significantly reduced after the removal of tumor mass. The CTAs identified among the analyzed HLA peptidomes provide new opportunities for personalized immunotherapy and for early diagnosis of GBM.

Purification of soluble HLA class I complexes from human serum or plasma deliver high quality immuno peptidomes required for biomarker discovery

Soluble human leukocyte antigen class I (sHLA)-peptide complexes have been suggested to play a role in the modulation of immune responses and in immune evasion of cancer cells. The set of peptides eluted from sHLA molecules could serve as biomarker for the monitoring of patients with cancer or other conditions. Here, we describe an improved sHLA peptidomics methodology resulting in the identification of 1816 to 2761 unique peptide sequences from triplicate analyses of serum or plasma taken from three healthy donors. More than 90% of the identified peptides were 8-11mers and 74% of these sequences were predicted to bind to cognate HLA alleles, confirming the quality of the resulting immunopeptidomes. In comparison to the HLA peptidome of cultured cells, the plasma-derived peptides were predicted to have a higher stability in complex with the cognate HLA molecules and mainly derived from proteins of the plasma membrane or from the extracellular space. The sHLA peptidomes can efficiently be characterized by using the new methodology, thus serving as potential source of biomarkers in various pathological conditions.

HLA-C and KIR combined genotype as new response marker for HBeAg-positive chronic hepatitis B patients treated with interferon-based combination therapy

Current treatment for chronic hepatitis B infection (CHB) consists of interferon-based therapy. However, for unknown reasons, a large proportion of patients with CHB do not respond to this treatment. Hence, there is a pressing need to establish response markers to select patients who will benefit from therapy and to spare potential nonresponders from unnecessary side effects of antiviral therapy. Here, we assessed whether HLA-C and KIR genotypes were associated with treatment outcome for CHB. Twelve SNPs in or near the HLA-C gene were genotyped in 86 CHB patients (41 HBeAg positive; 45 HBeAg negative) treated with peginterferon alfa-2a + adefovir. Genotyping of killer immunoglobin-like receptors (KIRs) was performed by SSP-PCR. One SNP in HLA-C (rs2308557) was significantly associated with combined response in HBeAg-positive CHB patients (P = 0.003). This SNP is linked to the HLA-C group C1 or C2 classification, which controls KIR binding. The combination of KIR2DL1 with its ligand HLA-C2 was observed significantly more often in HBeAg-positive patients with a combined response (13/14) than in nonresponders (11/27, P = 0.001). Patients with the KIR2DL1/C2 genotype had significantly higher baseline ALT levels (136 vs 50 U/L, P = 0.002) than patients without this combination. Furthermore, KIR2DL1-C2 predicted response independent of HBV genotype and ALT at baseline. HLA-C and KIR genotype is strongly associated with response in HBeAg-positive CHB patients treated with interferon-based therapy. In combination with other known response markers, HLA-C/KIR genotype could enable the selection of patients more likely to respond to interferon-based therapy.

Serum antibodies to human leucocyte antigen (HLA)-E, HLA-F and HLA-G in patients with systemic lupus erythematosus (SLE) during disease flares: Clinical relevance of HLA-F autoantibodies

T lymphocyte hyperactivity and progressive inflammation in systemic lupus erythematosus (SLE) patients results in over-expression of human leucocyte antigen (HLA)-Ib on the surface of lymphocytes. These are shed into the circulation upon inflammation, and may augment production of antibodies promoting pathogenicity of the disease. The objective was to evaluate the association of HLA-Ib (HLA-E, HLA-F and HLA-G) antibodies to the disease activity of SLE. The immunoglobulin (Ig)G/IgM reactivity to HLA-Ib and β2m in the sera of 69 German, 29 Mexican female SLE patients and 17 German female controls was measured by multiplex Luminex(®)-based flow cytometry. The values were expressed as mean flourescence intensity (MFI). Only the German SLE cohort was analysed in relation to the clinical disease activity. In the controls, anti-HLA-G IgG predominated over other HLA-Ib antibodies, whereas SLE patients had a preponderance of anti-HLA-F IgG over the other HLA-Ib antibodies. The disease activity index, Systemic Lupus Erythematosus Disease Activity Index (SLEDAI)-2000, was reflected only in the levels of anti-HLA-F IgG. Anti-HLA-F IgG with MFI level of 500-1999 was associated with active SLE, whereas inactive SLE revealed higher MFI (>2000). When anti-HLA-F IgG were cross-reactive with other HLA-Ib alleles, their reactivity was reflected in the levels of anti-HLA-E and -G IgG. The prevalence of HLA-F-monospecific antibodies in SLE patients was also associated with the clinical disease activity. Anti-HLA-F IgG is possibly involved in the clearance of HLA-F shed from lymphocytes and inflamed tissues to lessen the disease's severity, and thus emerges as a beneficial immune biomarker. Therefore, anti-HLA-Ib IgG should be considered as a biomarker in standard SLE diagnostics.

Behavior of soluble HLA-A, -B, -C and HLA-G molecules in patients with chronic hepatitis C virus infection undergoing pegylated interferon-α and ribavirin treatment: potential role as markers of response to antiviral therapy

The serum levels of soluble HLA class I antigens (sHLA-A, -B, -C and sHLA-G) were determined in 40 HCV genotype 1-infected patients before (T ₀), after 3, 6, and 12 months (T ₃, T ₆, and T ₁₂) of pegylated-IFN-α plus ribavirin therapy and 6 months (T ₁₈) after the end of treatment. Twenty patients were sustained virological responders (SVR), and 20 were non-responders (NR). sHLA-A, -B, -C levels at T ₀ were significantly higher in both SVR (mean 10.48 μg/ml) and NR (mean 11.87 μg/ml) patients as compared to healthy controls (mean 0.34 μg/ml, p < 0.0001) and HIV-infected subjects (mean 1.22 μg/ml, p < 0.0001). sHLA-G levels at T ₀ were significantly higher in SVR (mean 24.78 ng/ml) and NR (mean 24.93 ng/ml) patients as compared to healthy controls (mean 10.34 ng/ml, p = 0.015 and p = 0.014, respectively) but were lower as compared to HIV-infected subjects (mean 48.00 ng/ml, p < 0.0001). The levels of sHLA-A, -B, -C and sHLA-G significantly decreased in SVR from T ₀ to T ₁₈ (mean 1.64 and 1.43 ng/ml, respectively, p < 0.0001) and correlated with HCV-RNA, AST, ALT, γGT, and ALP levels. The determination of soluble HLA class I levels could be proposed as a surrogate marker to discriminate SVR and NR HCV-infected patients during PEG-IFN-α plus ribavirin therapy.

CD8low T-cell subpopulation is increased in patients with chronic hepatitis B virus infection

Recent studies suggest that CD8(+) T cells with down-regulated CD8 expression (CD3(+)CD8(low) T cells) represented as a distinct phenotype of CD8(+) T cells are increased and linked to disease severity in some chronically persistent infection, such as chronic HIV and parasite infection. However, the role of CD3(+)CD8(low) T cells in the context of chronic HBV infection is poorly understood. In this study, peripheral blood samples of 47 chronic hepatitis B patients and 19 healthy controls were collected and tested for the frequency and phenotype of CD8(low) T cells. The circulating CD8(low) T cells were significantly more frequent in the patients compared to those in healthy controls, and the CD8(low) T cells in the patients expressed less IFN-γ and more mTGF-β1 than those in the controls, suggesting their type-2 polarized and suppressive properties. Meanwhile, the concentrations of plasma soluble HLA class I molecules were found elevated in the patients, and positively associated with the frequencies of CD8(low) T cells. Furthermore, the CD8(low) T-cell frequency in the HLA-A2-positive patients (n=21) was found negatively correlated with the T-cell responsiveness against the HBc₁₈₋₂₇ peptide, the latter was impaired as revealed by IFN-γ Elispot assay. Our findings suggested that a better understanding of the involvement of CD8(low) T cells in chronically persistent HBV infection would add to our knowledge of the impaired T-cell response in the patients.

MHC class I antigen processing and presenting machinery: organization, function, and defects in tumor cells

The surface presentation of peptides by major histocompatibility complex (MHC) class I molecules is critical to all CD8(+) T-cell adaptive immune responses, including those against tumors. The generation of peptides and their loading on MHC class I molecules is a multistep process involving multiple molecular species that constitute the so-called antigen processing and presenting machinery (APM). The majority of class I peptides begin as proteasome degradation products of cytosolic proteins. Once transported into the endoplasmic reticulum by TAP (transporter associated with antigen processing), peptides are not bound randomly by class I molecules but are chosen by length and sequence, with peptidases editing the raw peptide pool. Aberrations in APM genes and proteins have frequently been observed in human tumors and found to correlate with relevant clinical variables, including tumor grade, tumor stage, disease recurrence, and survival. These findings support the idea that APM defects are immune escape mechanisms that disrupt the tumor cells' ability to be recognized and killed by tumor antigen-specific cytotoxic CD8(+) T cells. Detailed knowledge of APM is crucial for the optimization of T cell-based immunotherapy protocols.

Elevated soluble HLA II protein levels in patients with alpha-1 antitrypsin deficiency with or without COPD

Elevated levels of human leukocyte antigen (HLA) proteins have been reported in several pathologic conditions that are associated with increased concentrations of white blood cells (e.g., infection, inflammation, and lymphoproliferative disorders). The mechanisms by which HLA proteins are solubilized from cell membranes are insufficiently understood. We hypothesized that HLA proteins may be cleaved from cell membranes by insufficiently inhibited leukocytic elastase, as expected in alpha-1 antitrypsin deficiency (A1ATD), resulting in elevated plasma levels of soluble HLA (sHLA) proteins. Using an enzyme-linked immunosorbent assay, we measured sHLA II levels in the peripheral blood of patients with A1ATD with or without co-existing chronic obstructive pulmonary disease (COPD), with COPD only, and in a control group. Mean (±SD) sHLA II plasma levels were 110 ± 200 pg/mL in patients with A1ATD and COPD (Group 1), 10 ± 30 pg/mL in patients with COPD without A1ATD (Group 2), 70 ± 90 pg/mL in patients with A1ATD without COPD (Group 3), and 10 ± 30 pg/mL in healthy donors (Group 4). Soluble HLA II plasma levels were significantly higher in Group 1 (P = .001) and Group 3 (P = .002) versus Group 4. Our preliminary results suggest that leukocytic elastase and probably other proteinases solubilize HLA proteins from cell membranes. This mechanism would operate in inflammation with elevated leukocytic elastase levels but more so with inflammation and A1ATD, where elastase would be insufficiently inhibited. If this mechanism is verified, plasma sHLA levels could potentially be used to measure cell damage due to proteinases and, therefore, for monitoring the therapeutic efficacy of alpha-1 antitrypsin (A1AT) augmentation therapy.

The β2-microglobulin-free heterodimerization of rhesus monkey MHC class I A with its normally spliced variant reduces the ubiquitin-dependent degradation of MHC class I A

The MHC class I (MHC I) molecules play a pivotal role in the regulation of immune responses by presenting antigenic peptides to CTLs and by regulating cytolytic activities of NK cells. In this article, we show that MHC I A in rhesus macaques can be alternatively spliced, generating a novel MHC I A isoform (termed "MHC I A-sv1") devoid of α(3) domain. Despite the absence of β2-microglobulin (β2m), the MHC I A-sv1 proteins reached the cell surface of K562-transfected cells as endoglycosidase H-sensitive glycoproteins that could form disulfide-bonded homodimers. Cycloheximide-based protein chase experiments showed that the MHC I A-sv1 proteins were more stable than the full-length MHC I A in transiently or stably transfected cell lines. Of particular interest, our studies demonstrated that MHC I A-sv1 could form β2m-free heterodimers with its full-length protein in mammalian cells. The formation of heterodimers was accompanied by a reduction in full-length MHC I A ubiquitination and consequent stabilization of the protein. Taken together, these results demonstrated that MHC I A-sv1 and MHC I A can form a novel heterodimeric complex as a result of the displacement of β2m and illustrated the relevance of regulated MHC I A protein degradation in the β2m-free heterodimerization-dependent control, which may have some implications for the MHC I A splice variant in the fine tuning of classical MHC I A/TCR and MHC I A/killer cell Ig-like receptor interactions.

Comparative analysis of serum proteomes of degenerative scoliosis

Degenerative scoliosis (DS) is an important degenerative lumbar disease causing spinal dysfunction and affecting the quality of life of the elderly, and is associated not only with severe back or leg pain but also with complicated surgical outcomes. The pathogenesis of DS is still unknown. Therefore, it is very important to ascertain the etiology of degenerative scoliosis and establish related molecular markers predicting and controlling the scoliosis. For the first time, we used two-dimensional fluorescence DIGE to compare the serum proteome profiles of 12 DS patients and controls. Proteins found to be differentially expressed were identified by MALDI-TOF mass spectrometric analysis, coupled with database interrogation. Eleven spots that were differentially expressed in the sera of DS patients were found, and eight gene products were identified among these spots. Clusterin, CLU cDNA FLJ57622, ALB cDNA FLJ50830, Hypothetical short protein, HLA-A MHC class 1 antigen. (Fragment), ALB 23 kDa protein, Isoform 1 of G protein-regulated inducer of neurite outgrowth 1 (GPRIN I)and Ficolin-3 were down-regulated in the sera of DS patients. The decreased levels of Clusterin and Ficolin-3 were confirmed by Western blot. The information obtained with this proteomic analysis will be very useful in understanding the pathophysiology of DS as well as in finding candidates as drug targets of DS. These results may provide a novel approach for the pathogenesis study of DS.

A potential role for shed soluble major histocompatibility class I molecules as modulators of neurite outgrowth

The neurobiological activities of classical major histocompatibility class I (MHCI) molecules are just beginning to be explored. To further examine MHCI's actions during the formation of neuronal connections, we cultured embryonic mouse retina explants a short distance from wildtype thalamic explants, or thalami from transgenic mice (termed “NSE-D^b”) whose neurons express higher levels of MHCI. While retina neurites extended to form connections with wildtype thalami, we were surprised to find that retina neurite outgrowth was very stunted in regions proximal to NSE-D^b thalamic explants, suggesting that a diffusible factor from these thalami inhibited retina neurite outgrowth. It has been long known that MHCI-expressing cells release soluble forms of MHCI (sMHCI) due to the shedding of intact MHCI molecules, as well as the alternative exon splicing of its heavy chain or the action proteases which cleave off it's transmembrane anchor. We show that the diffusible inhibitory factor from the NSE-D^b thalami is sMHCI. We also show that COS cells programmed to express murine MHCI release sMHCI that inhibits neurite outgrowth from nearby neurons in vitro. The neuroinhibitory effect of sMHCI could be blocked by lowering cAMP levels, suggesting that the neuronal MHCI receptor's signaling mechanism involves a cyclic nucleotide-dependent pathway. Our results suggest that MHCI may not only have neurobiological activity in its membrane-bound form, it may also influence local neurons as a soluble molecule. We discuss the involvement of complement proteins in generating sMHCI and new theoretical models of MHCI's biological activities in the nervous system.

Behavior of non-classical soluble HLA class G antigens in human immunodeficiency virus 1-infected patients before and after HAART: comparison with classical soluble HLA-A, -B, -C antigens and potential role in immune-reconstitution

We have reported that serum level of soluble HLA-A, -B, -C (sHLA-A,-B,-C) antigens is elevated in HIV-infected subjects and decreases after antiretroviral therapy (HAART). In this study, we measured the levels of soluble HLA-G (sHLA-G) antigens in a cohort of HIV-infected patients before and during HAART. sHLA-G and sHLA-A, -B, -C levels were significantly elevated in HIV-infected subjects as compared with controls before antiretroviral treatment and significantly decreased after 36 months of HAART. sHLA-G levels were correlated with sHLA-A, -B, -C levels, the decrease of plasma HIV-RNA level, the increase of CD4+ T-lymphocyte number and the decrease of CD8+ T-lymphocyte number. These results suggest that the measurement of sHLA-G and sHLA-A, -B, -C antigen serum levels might represent a useful surrogate marker to monitor virological response and immune reconstitution in HIV-positive subjects undergoing HAART treatment.

Soluble serum HLA-G and HLA-A, -B, -C molecules in patients with seasonal allergic rhinitis exposed to pollens

BACKGROUND

Allergic rhinitis (AR) is characterized by a Th2 polarized immune response and soluble HLA (sHLA) molecules play an immunomodulatory role in this response. Previously, it has been reported that these molecules are increased in sera of patients with pollen-induced allergic rhinitis studied outside the pollen season. To date, however, no study has investigated there in AR patients during the pollen season.

OBJECTIVE

The aim of this study was to evaluate serum sHLA-G and sHLA-A, -B, -C levels in both AR patients and healthy controls.

METHODS

60 symptomatic allergic patients were enrolled. A group of 50 healthy subjects was included as a control. Serum sHLA-G and sHLA-A, -B, -C levels were determined by an immunoenzymatic method. Allergy severity was assessed by VAS for symptoms and drug use.

RESULTS

Allergic patients had significantly higher levels of both sHLA-G (p<0.001) and sHLA-A, -B, -C (p=0.001) than normal controls. In addition, there was a very strong correlation between sHLA-G levels and clinical severity.

CONCLUSION

The present study confirms evidence that serum sHLA-G and sHLA-A, -B, -C molecules are significantly increased in patients with pollen-induced AR also during the pollen season. Moreover, sHLA-G might be considered as a biomarker for assessing clinical severity.

Sublingual immunotherapy reduces soluble HLA-G and HLA-A,-B,-C serum levels in patients with allergic rhinitis

Allergic rhinitis (AR) is characterized by Th2 polarized immune response. Soluble HLA (sHLA) molecules play an immunomodulatory activity. Specific immunotherapy is the only causal treatment for AR. So far no study investigated the effect of sublingual immunotherapy (SLIT) on sHLA molecules. The aim of the study was to evaluate sHLA-G and sHLA-A,-B,-C serum levels in AR patients with pollen allergy before and after a pre-seasonal course of SLIT. Forty AR patients with pollen allergy were enrolled and they assumed a pre-seasonal SLIT course for 3 months. Serum sHLA-G and sHLA-A,-B,-C and IFN-gamma and IL-4 levels were determined by ELISA method at baseline and 3 months after the end of the SLIT course. Symptoms severity was assessed by a Visual Analogue Scale. Both sHLA-G and sHLA-A,-B,-C levels significantly diminished (p<0.0001 for both) after SLIT. Moreover, there was a highly significant relationship between the serum levels of these two soluble molecules (r=0.84). Significant relationship between symptoms evaluated by VAS and change of sHLA molecules was also evidenced (r=0.60 and 0.63). Serum cytokines were not affected by SLIT. Therefore, this preliminary study provides the first evidence that both sHLA-G and sHLA-A,-B,-C levels are significantly reduced by SLIT in AR patients with pollen allergy. Therefore, the clinical implication of this study is that these soluble molecules might be interpreted as biomarker of response to SLIT.

Soluble HLA-G and HLA-A,-B,-C serum levels in patients with allergic rhinitis

BACKGROUND

Allergic rhinitis (AR) is characterized by Th2-polarized immune response. Soluble HLA (sHLA) molecules play an immunomodulatory activity. So far, however, no study investigated them in AR.

OBJECTIVE

The aim of this study was to evaluate sHLA-G and sHLA-A,-B,-C serum levels in AR patients with pollen allergy and in a group of healthy controls.

METHODS

Forty-nine AR patients were enrolled. A group of healthy nonallergic subjects was considered as control. sHLA-G and sHLA-A,-B,-C serum levels were determined by immunoenzymatic method. The study was conducted during the winter, such as outside the pollen season.

RESULTS

Allergic patients had significantly higher levels of both sHLA-G (P < 0.0001) and sHLA-A,-B,-C (P = 0.011) molecules than normal controls. Moreover, there was a significant relationship between these two soluble molecules (r = 0.69) in allergic patients.

CONCLUSION

The present study provides the first evidence that both sHLA-G and sHLA-A,-B,-C serum levels are significantly increased in AR patients with pollen allergy.

Tumor escape mechanisms: potential role of soluble HLA antigens and NK cells activating ligands

The crucial role played by human leukocyte antigen (HLA) antigens and natural killer (NK)-cell-activating ligands in the interactions of malignant cells with components of the host's immune system has stimulated interest in the characterization of their expression by malignant cells. Convincing evidence generated by the immunohistochemical staining of surgically removed malignant lesions with monoclonal antibodies recognizing HLA antigens and NK-cell-activating ligands indicates that the surface expression of these molecules is frequently altered on malignant cells. These changes appear to have clinical significance because in some types of malignant disease they are associated with the histopathological characteristics of the lesions as well as with disease-free interval and survival. These associations have been suggested to reflect the effect of HLA antigen and NK-cell-activating ligand abnormalities on the interactions of tumor cells with antigen-specific cytotoxic T lymphocytes (CTL) and with NK cells. Nevertheless, there are examples in which disease progresses in the face of appropriate HLA antigen and/or NK-cell-activating ligand as well as tumor antigen expression by malignant cells and of functional antigen-specific CTL in the investigated patient. In such scenarios, it is likely that the tumor microenvironment is unfavorable for CTL and NK cell activity and contributes to tumor immune escape. Many distinct escape mechanisms have been shown to protect malignant cells from immune recognition and destruction in the tumor microenvironment. In this article, following the description of the structural and functional characteristics of soluble HLA antigens and NK-cell-activating ligands, we will review changes in their serum level in malignant disease and discuss their potential role in the escape mechanisms used by tumor cells to avoid recognition and destruction.

Relationship between soluble HLA-G and HLA-A,-B,-C serum levels, and interferon-gamma production after sublingual immunotherapy in patients with allergic rhinitis

Allergic rhinitis (AR) is characterized by a T-helper (Th)-2 (Th2) polarized immune response. Soluble human leukocyte antigen (sHLA) molecules play an immunomodulatory role. Specific immunotherapy is the only causal treatment for AR and is able to shift the immune response to Th1 polarization. The aim of this study was to evaluate the relationship between sHLA-G and sHLA-A,-B,-C serum levels and interferon-gamma (IFN-gamma) production in AR patients with pollen allergy before and after a preseasonal course of sublingual immunotherapy (SLIT). A total of 40 AR patients with pollen allergy were enrolled and given a course of preseasonal SLIT for 3 months. Serum sHLA-G and sHLA-A,-B,-C levels were determined by enzyme-linked immunoabsorbent assay, and cell production of IFN-gamma was evaluated by enzyme-linked immunoabsorbent spot assay at baseline and 3 months after the end of the SLIT course. There was a significant relationship between sHLA-G serum level change and IFN-gamma increase as well as between sHLA-A,-B,-C level change and IFN-gamma increase after SLIT. The present study provides the first published evidence that the reduction of sHLA molecules serum levels and the increased IFN-gamma production after SLIT in AR patients with pollen allergy are significantly related phenomena.

Soluble MHC class I chain-related protein B serum levels correlate with disease activity in relapsing-remitting multiple sclerosis

Recent studies demonstrated that dysregulation of NKG2D and its ligands, leading to activation of autoreactive effector cells, can trigger autoimmune diseases, but soluble forms of these ligands can downmodulate NKG2D expression in T effector cells. We investigated the presence of soluble major histocompatibility complex class I chain-related A or B (MICA or MICB) molecules in sera of multiple sclerosis (MS) patients and whether they play a role in the progression of the disease. Although soluble MICA serum levels did not differ, soluble MICB serum levels were higher in MS patients compared with controls. Moreover, the highest MICB levels were in MS patients during relapses. Using immunohistochemistry techniques, it was possible to locate MIC expression in neurons of MS demyelinating plaques that were intracellularly accumulated. Elevated soluble MICB levels exist in serum of multiple sclerosis patients related with disease activity. This may contribute to the modulation of immune response activity during relapses.

Behavior of serum human major histocompatibility complex class I antigen levels in human immunodeficiency virus-infected patients during antiretroviral therapy: correlation with clinical outcome

Human major histocompatibility complex class I antigens (HLA-A, -B, and -C) are heterodimeric molecules composed of a alpha heavy chain noncovalently associated with an invariant protein known as beta(2)-microglobulin. Beside being expressed on the membrane of the large majority of nucleated cells, HLA class I antigens are evident in serum (sHLA-I). We have previously detected a significant increase in the serum level of beta(2)-microglobulin-associated HLA-I antigens in human immunodeficiency virus (HIV)-infected patients compared with HIV-negative controls. The introduction of highly active antiretroviral therapy (HAART) modified the clinical course of the disease and decreased the acquired immunodeficiency syndrome-related morbidity and mortality. Therefore, we measured the levels of sHLA-I antigens in 64 HIV-infected patients before and during HAART treatment and correlated them with the immunological and virological response to antiretroviral treatment. Serum sHLA-I antigen level was elevated in all HIV-infected patients before and significantly decreased after 36 months of HAART treatment, correlating with the decrease of plasma HIV-RNA level and with the increase of CD4+ T-lymphocyte number. These results suggest that the measurement of sHLA-I antigens serum level might represent a useful surrogate marker to monitor HIV-positive patients undergoing HAART treatment.

Soluble HLA-G: Are they clinically relevant?

HLA-G is a non-classical HLA-class Ib molecule with multiple immunoregulatory properties. Its main function in physiological conditions is to abrogate maternal NK cell activity against foetal tissue and to establish immune tolerance at maternal-foetal interface. HLA-G is expressed not only as a membrane bound molecule on the surface of cells, but also as a soluble moiety in body fluids. The major isoforms of HLA-G present in serum are soluble HLA-G1 and HLA-G5 which are generated by shedding or proteolytic cleavage of the membrane bound isoform and by secretion of a soluble isoform, respectively. Here we review the data about soluble HLA-G (sHLA-G) serum levels in different pathological conditions, including immune-mediated disorders, transplantation and malignancies. In particular, we focus on sHLA-G expression and function in human neuroblastoma, a pediatric tumor, with special emphasis on a novel potential immuno escape mechanism utilized by NB to instruct monocytes to produce and release sHLA-G. Finally, the potential clinical relevance of sHLA-G serum levels is discussed.

In vivo apoptosis of CD8(+) lymphocytes in acute myeloid leukemia patients: involvement of soluble HLA-I and Fas ligand

In this study, we show that high serum levels of soluble human leukocyte antigens (HLA) class I molecules (sHLA-I, range: 0.7-1.7 micro g/ml) and soluble Fas ligand (FasL, range: 0.4-1.9 ng/ml) are detected in patients with acute myeloid leukemia (AML) at diagnosis, compared with healthy donors (HD) (sHLA-I, range: 0.1-0.6 micro g/ml; sFasL, range: 0.1-0.4 ng/ml). Patients' sera were able to induce transcription and secretion of FasL in CD8(+) T cells, followed by apoptosis in vitro; this apoptosis was inhibited by anti-HLA-I-specific monoclonal antibodies, suggesting that sHLA-I is responsible for cell death. These findings closely relate to the in vivo upregulation of FasL transcription observed in peripheral blood (PB) lymphocytes from AML patients; in the same cells, mRNA for the antiapoptotic proteins Bcl-2 and Bcl-x(L) was downregulated. Interestingly, caspase-8 and caspase-3, both downstream mediators of death receptor-induced apoptosis, were activated in CD8(+) cells of AML patients; one-third of these cells were already apoptotic in vivo, at variance with lymphocytes of HD. These data strongly suggest that in AML, increased levels of sHLA-I molecules may contribute to the elimination of potentially anti-tumor effector cells through a FasL/Fas interaction.

Soluble HLA revisited

The goal of this editorial is to revisit soluble human leukocyte antigens (sHLA) and to highlight the findings reported by Albitar et al. in this issue on the relation between sHLA levels in Non-Hodgkin's Lymphoma (NHL) and Hodgkin's Disease (HD). We will review key aspects of sHLA including soluble HLA-G, which has received a lot of attention in recent publications. We will then address the role of sHLA in lymphoproliferative diseases and in solid organ tumors. Lastly, we will comment on the results of Albitar et al. and their relevance to clinical application in NHL.

Apoptosis of antigen-specific T lymphocytes upon the engagement of CD8 by soluble HLA class I molecules is Fas ligand/Fas mediated: evidence for the involvement of p56lck, calcium calmodulin kinase II, and Calcium-independent protein kinase C signaling pathways and for NF-kappaB and NF-AT nuclear translocation

The binding of soluble HLA class I (sHLA-I) molecules to CD8 on EBV-specific CTL induced up-regulation of Fas ligand (FasL) mRNA and consequent sFasL protein secretion. This, in turn, triggered CTL apoptosis by FasL/Fas interaction. Molecular analysis of the biochemical pathways responsible for FasL up-regulation showed that sHLA-I/CD8 interaction firstly induced the recruitment of src-like p56(lck) and syk-like Zap-70 protein tyrosine kinases (PTK). Interestingly, p59(fyn) was activated upon the engagement of CD3/TCR complex but not upon the interaction of sHLA-I with CD8. In addition, sHLA-I/CD8 interaction, which is different from signaling through the CD3/TCR complex, did not induce nuclear translocation of AP-1 protein complex. These findings suggest that CD8- and CD3/TCR-mediated activating stimuli can recruit different PTK and transcription factors. Indeed, the engagement of CD8 by sHLA-I led to the activation of Ca2+ calmodulin kinase II pathway, which eventually was responsible for the NF-AT nuclear translocation. In addition, we found that the ligation of sHLA-I to CD8 recruited protein kinase C, leading to NF-kappaB activation. Both NF-AT and NF-kappaB were responsible for the induction of FasL mRNA and consequent CTL apoptosis. Moreover, FasL up-regulation and CTL apoptotic death were down-regulated by pharmacological specific inhibitors of Ca2+/calmodulin/calcineurin and Ca2+-independent protein kinase C signaling pathways. These findings clarify the intracellular signaling pathways triggering FasL up-regulation and apoptosis in CTL upon sHLA-I/CD8 ligation and suggest that sHLA-I molecules can be proposed as therapeutic tools to modulate immune responses.

Cyclosporin A regulates human NK cell apoptosis induced by soluble HLA-I or by target cells

Human natural killer (NK) cells are effectors of innate immunity, capable of killing transformed or virus-infected cells and producing pro-inflammatory cytokines. Soluble molecules of HLA-I (sHLA-I), which are significantly increased in the serum of patients affected by auto-immune or infectious or neoplastic diseases, induce NK cell apoptosis interacting with its ligands, such as CD8 or the activating isoforms of members of inhibitory superfamily receptors (IRS). This cell death is accompanied by the release of large amounts of interferon-gamma. NK cells can kill autologous target cells, including antigen presenting cells or infected or tumor cells, by engaging the natural cytotoxicity receptors (NCR) NKp30, or NKp44 and NKp46. Again, the binding between NCR on NK cells and their putative ligands on targets leads to NK cell apoptosis. FasL produced and secreted by NK cells is responsible for the NK cell apoptosis induced by either HLA-I receptors or NCR. Interestingly, cyclosporin A (CsA) blocks NK cell death consequent to interaction with target cells or with sHLA-I, without affecting the activation of cytolysis. This would indicate that CsA can maintain NK cell-dependent innate immunity by prolonging NK cell survival in an hostile environment in the presence of sHLA-I or target cells.

Regulation of γδ T cell survival by soluble HLA-I: Involvement of CD8 and activating killer Ig-like receptors

We show that human Vdelta1 or Vdelta2 T lymphocytes secrete FasL and undergo apoptosis upon incubation with soluble HLA (sHLA)-I or after cross-linking of CD8, with a kinetics different from that observed following ligation of TCR. sHLA-I-induced apoptosis was blocked by anti-CD8 mAb; on the other hand, sHLA-I was not effective in CD8- clones, while an HLA-I mutated in the alpha3 domain, responsible for CD8 binding, was not functional on CD8+ clones. Purified sHLA-Cw3 or -Cw4 alleles, isolated from the Cw3- or Cw4-transfected 721.221 lymphoblastoid cell line, triggered gammadelta T cell apoptosis, interacting with the specific receptors CD158j/KIR2DS2 or CD158 h/KIR2DS1, respectively, also known as activating isoforms of killer Ig-like receptors (KIR). Again, this effect was dependent on FasL secretion and it was blocked by specific mAb to KIR2DS2 or KIR2DS1. The engagement of CD8 or activating KIR also triggered the production of TNF-alpha. Noteworthy, sHLA-I molecules synergize with antigen-mediated activation of Vdelta2 T cells: Indeed, Vdelta2 T lymphocytes produced TNF-alpha when stimulated with isopentenyl pyrophosphate, and this effect was enhanced by sHLA-I. These findings suggest that sHLA-I can regulate gammadelta T cell survival and that activating KIR may amplify antigen-specific Vdelta2 T cell responses.

CMV-infected allogeneic endothelial cells initiate responder and bystander donor HLA class I release via the metalloproteinase cleavage pathway

Although cytomegalovirus (CMV) interferes with major histocompatibility expression in infected cells, both host and donor soluble human leukocyte antigen class I (sHLA-I) are often released into the serum of transplant recipients during CMV infection and may contribute to anti-HLA antibody production and graft rejection. We hypothesized that CMV infection of endothelial cells (EC) induces host T cells to release interferon (IFN)-gamma, which in turn drives the metalloproteinase (MPase)-cleavage pathway of sHLA-I generation in "bystander" uninfected ECs. To test this hypothesis, cultures of peripheral blood mononuclear cells (PBMCs) and either uninfected ECs or CMV-infected ECs (EC/CMV) were established and supernatants were tested in enzyme-linked immunosorbent assay for sHLA-I. Responder PBMC became activated and released sHLA-I via the MPase pathway when stimulated with allogeneic EC/CMV; the sHLA-I release was contact dependent and cytokine independent. In transwell cultures, IFN-gamma released by PBMCs in response to EC/CMV stimulated a release of sHLA-I from uninfected allogeneic ECs across the transwell; this release was also MPase dependent. This implies that CMV infection within the transplanted allograft will not only stimulate the release of self HLA from responding PBMCs, but will also stimulate the release of donor sHLA-I from uninfected bystander ECs, both via the class I MPase-pathway.

Soluble HLA class I and HLA-DR plasma levels in patients with anterior uveitis

Anterior uveitis (AU) is an autoimmune disease frequently associated with HLA-B27 antigen. Because of the immune regulatory properties of soluble human leukocyte antigen (sHLA) molecules, we quantified sHLA class I (sHLA-I) and sHLA-DR plasma levels in HLA-typed AU patients (n = 60). Randomly selected healthy individuals (n = 128) and HLA-B27 antigen-positive individuals (n = 24) with HLA phenotype frequencies similar to the HLA-B27 antigen-positive AU patients served as control panels. As expected, HLA-B27 phenotype was significantly increased in AU patients (n = 60), compared to healthy controls. Mean sHLA-I levels in AU patients were slightly higher than in randomly selected healthy controls. Regarding AU subgroups, elevated sHLA-I levels were only found in HLA-B27 antigen-negative patients. Compared to controls, sHLA-DR levels were significantly increased in AU patients and the subgroups of HLA-B27 antigen-negative and -positive patients but not Fuchs' heterochromic cyclitis (FHC). AU patients negative for HLA-B27 antigen with a chronic course had higher sHLA-DR levels than those with an acute course. The presence of associated systemic diseases in AU patients was related to elevated sHLA-DR levels. Secretion of sHLA-DR in blood differs among the various forms of AU. Systemic immune activation was present in AU but not in FHC.

Beneficial effect of interferon-β 1b treatment in patients with relapsing–remitting multiple sclerosis is associated with an increase in serum levels of soluble HLA-I molecules during the first 3 months of therapy

It has recently become clear that interferon-beta (IFN-beta) treatment is effective in ameliorating relapsing-remitting multiple sclerosis (RRMS) through an as yet unidentified mechanism. As there is no recognisable biological indicator to predict responsiveness to IFN-beta treatment, we have investigated fluctuations in serum sHLA-I levels in MS patients undergoing IFN-beta 1b therapy. Serum sHLA-I concentrations measured by enzyme-linked immunosorbent assay (ELISA) were assessed at baseline and, longitudinally, over a period of 18 months after the start of treatment in 29 RRMS patients grouped as responders and nonresponders according to their clinical response to IFN-beta 1b therapy. Thirty-nine healthy volunteers served as controls. Serum sHLA-I concentrations were significantly higher (p<0.001) in pretreated RRMS patients than in healthy donors. In MS patients, changes in mean serum levels of sHLA-I from baseline showed a temporal pattern characterized by a strong increase in the first trimester of treatment, a return toward basal values in the following 6 months, a slight decline at 12th and 15th months and a further moderate increase at the 18th month. Mean serum sHLA-I levels were significantly more elevated in responders than in nonresponders at the first (p<0.02), second (p<0.01), and at third (p<0.02) months after the beginning of treatment and significantly lower (p<0.01) at the time of relapses in comparison to baseline values. Overall, these results seem to indicate that IFN-beta 1b can modulate fluctuations in serum sHLA-I levels and argue in favour of a potential role for serum levels of sHLA-I as a sensitive marker to monitor response to IFN-beta treatment in MS.

Direct interaction of major histocompatibility complex class II-derived peptides with class Ia phosphoinositide 3-kinase results in dose-dependent stimulatory effects

Peptides corresponding to residues 65-79 of human lymphocyte antigen class II sequence (DQA*03011) are cell-permeable and at high concentrations block activation of protein kinase B/Akt and p70-S6 kinase in T-cells, effects attributed to inhibition of phosphoinositide (PI) 3-kinase activity. To understand the molecular basis of this, we analyzed the effect this peptide had on activity of class I PI 3-kinases. Although there was no effect on the activity of class Ib PI 3-kinase or on the protein kinase activity of class I PI 3-kinases, there was a biphasic effect on lipid kinase activity of the class Ia enzymes. There was an inhibition of activity at higher peptide concentrations because of a formation of insoluble complexes between peptide and enzyme. Conversely, at lower peptide concentrations there was a profound activation of PI 3-kinase activity of class Ia PI 3-kinases. Studies of peptide variants revealed that all active peptides conform to heptad repeat motifs characteristic of coiled-coil helices. Surface plasmon resonance studies confirmed direct sequence-specific binding of active peptide to the p85alpha adapter subunit of class Ia PI 3-kinase. Active peptides also activated protein kinase B and extracellular signal-regulated kinase (ERK) in vivo in a wortmannin-sensitive manner while reducing recoverable cellular p85 levels. These results indicate that the human lymphocyte antigen class II-derived peptides regulate PI 3-kinase by direct interaction, probably via the coiled-coil domain. These peptides define a novel mechanism of regulating PI 3-kinase and will provide a useful tool for specifically dissecting the function of class Ia PI 3-kinase in cells and for probing structure-function relationships in the class Ia PI 3-kinase heterodimers.

Soluble HLA-DR and soluble CD95 ligand levels in pregnant women with antiphospholipid syndromes

Antiphospholipid syndrome (APS) is a severe complication in pregnancy that can lead to fetal death in the second or third trimester. As soluble HLA-DR (sHLA-DR) molecules are reported to be implicated in the etiology of pregnancy disorders and of autoimmune diseases, we studied sHLA-DR plasma levels in pregnant women with APS (n = 14) and in women with normal pregnancy (n = 15), in women with high-risk pregnancies such as preeclampsia (PE; n = 20) and intrauterine growth retardation (IUGR; n = 10) and in fertile non-pregnant women (n = 29). The sHLA-DR levels of pregnant women were assessed during the third trimester, at labor, in the first week, and in the third month of puerperium. The results obtained were compared with soluble CD95 ligand (sCD95L), an important signal molecule in the apoptosis pathway. The sHLA-DR levels in pregnant women with APS were approximately three times higher (mean 1.48 +/- 0.15 microg/ml) during the whole observation period than in fertile non-pregnant women (0.54 +/-.06 microg/ml) and nearly double in women with high risk (PE, 0.91 +/- 14 microg/ml; IUGR, 0.94 +/-.21 microg/ml) and in normal pregnancies (0.74 +/- 0.13 microg/ml). Furthermore, sHLA-DR levels of pregnant women with APS were positively correlated with the serum concentration of anti-anticardiolipin immunoglobulin G antibodies. For sCD95L plasma levels, no substantial variations were found among the different groups above. In pregnant women with APS, however, sHLA-DR levels were positively correlated with sCD95L levels. Further studies should clarify the functional involvement of sHLA-DR molecules in the induction of CD95/CD95L-mediated apoptosis pathway that may play a crucial role in the pathology of pregnancies complicated by APS.

Soluble HLA class I induces NK cell apoptosis upon the engagement of killer-activating HLA class I receptors through FasL-Fas interaction

The engagement of the activating isoforms of C-type lectin inhibitory receptor (CLIR) or killer Ig-like receptor (KIR) by their natural ligands, represented by soluble HLA-I (sHLA-I) molecules, induced programmed cell death of natural killer (NK) cells. Indeed, NK cell apoptosis elicited by either putative HLA-E and HLA-F (sHLA-I non-A, -B, -C, and -G) or sHLA-I-Cw4 or -Cw3 from untransfected or -Cw4 or -Cw3 alleles transfected HLA-A(-), B(-), C(-), G(-), E(+), F(+) 721.221 lymphoblastoid cell line, respectively, was blocked by covering the corresponding activating receptor with either anti-CLIR- or anti-KIR-specific monoclonal antibodies (mAbs). After sHLA-I-activating receptor interaction, NK cells produced and released Fas ligand (FasL), which in turn led to NK cell apoptosis by interacting with Fas at the NK cell surface. Blocking anti-Fas mAb, or anti-FasL mAb, inhibited sHLA-I-mediated apoptosis via activating receptor in NK cell clones. This apoptosis was inhibited by NK cell treatment with cyclosporin A, whereas this drug had no effect on activating receptor-mediated activation of cytolysis. Conversely, concanamycin A, an inhibitor of vacuolar type H(+)-adenosine triphosphatase (H(+)-ATPase) of granules, inhibited activating receptor-induced NK cell cytolysis, suggesting that activating receptor-mediated apoptosis and cytolysis can use different intracellular pathways. Furthermore, a large amount of interferon-gamma (IFN-gamma) was detectable in culture supernatant of activating receptor(+) NK cells incubated with the appropriate sHLA-I ligand. Again, cyclosporin A, but not concanamycin A, strongly reduced activating receptor-mediated IFN-gamma production. This suggests that activating receptor-induced apoptosis of NK cells could play a role in eliminating potentially harmful NK cell clones and, at the same time, it leads to production of IFN-gamma, an antiviral cytokine able to amplify immune responses.

Clinical and MRI disease activity in multiple sclerosis are associated with reciprocal fluctuations in serum and cerebrospinal fluid levels of soluble HLA class I molecules

The goal of our study was to clarify the contribution of soluble human leukocyte antigens class I (sHLA-I) in multiple sclerosis (MS) immune dysregulation. We retrospectively evaluated by ELISA cerebrospinal fluid (CSF) and serum sHLA-I levels in 79 relapsing-remitting (RR), 26 secondary progressive (SP) and 15 primary progressive (PP) MS patients stratified according to clinical and Magnetic Resonance Imaging (MRI) evidence of disease activity. One hundred and nine patients with other inflammatory neurological disorders (OIND), 88 with noninflammatory neurological disorders (NIND) and 82 healthy donors were used as controls. An intrathecal synthesis of sHLA-I detected by a specific index was significantly more consistent in MS than in controls, with more pronounced values in MS patients with relapses and MRI enhancing brain lesions. A decrease in serum sHLA-I concentrations was observed in MS patients with demyelinating attacks, while an increase in CSF levels of sHLA-I was found in MS patients with lesional activity on MRI scans. This association between intrathecal synthesis and reciprocal fluctuations of CSF and serum levels of sHLA-I in clinically and MRI active MS seems to suggest a potential role for CSF and serum levels of sHLA-I as a sensitive marker of immune activation taking place both intrathecally and systemically in MS.

Soluble HLA class I molecules induce natural killer cell apoptosis through the engagement of CD8: evidence for a negative regulation exerted by members of the inhibitory receptor superfamily

Herein, we show that CD8(dull), CD8(intermediate), and CD8(bright) natural killer (NK) cell clones can be identified. Triggering of CD8 with its natural ligand(s), represented by soluble HLA class I (sHLA-I), isolated either from serum of healthy donors or from HLA-I(-) 721.221 lymphoblastoid cell line transfected with HLA-A2, -Cw4, and -Bw46 alleles, or HLA-G1 leads to NK cell apoptosis. The magnitude of this effect directly correlated with the level of CD8 expression. sHLA-I-induced apoptosis depends on the interaction with CD8, as it was inhibited by masking this molecule with specific monoclonal antibodies (mAbs). Moreover, sHLA-I or CD8 cross-linking with specific mAbs elicited intracellular calcium increases, Fas ligand (FasL) messenger RNA transcription, and FasL secretion, which were needed for delivering the death signal. Indeed, this apoptosis was inhibited by preincubation of NK cell clones with Fas or FasL antagonist mAbs, indicating that the Fas/FasL pathway is involved. Furthermore, members of the inhibitory receptor superfamily, such as CD94/NKG2 complex or killer inhibitory receptors, were shown to exert an inhibitory effect on sHLA-I-mediated apoptosis and secretion of FasL. These findings suggest that interaction between sHLA-I and CD8 evokes an apoptotic signal that is down-regulated by inhibitory receptor superfamily that function as survival receptors in NK cells.

Rapid decreases in donor-specific cytotoxic T lymphocyte precursor frequencies and graft outcome after liver and lung transplantation

BACKGROUND

A decrease in donor-specific T cell precursor frequencies as seen late, one or more years, after transplantation is assumed to reflect transplantation tolerance, a condition important for long term acceptance of the allograft. However, such late decreases also occur in recipients that developed chronic transplant dysfunction questioning its relevance in transplantation tolerance. We investigated whether early, i.e., the first 6 months, decreases in donor-specific T cell precursor frequencies reflect transplantation tolerance and predict graft outcome after liver and lung transplantation.

METHODS

Donor and third party specific cytotoxic (CTLp) and helper T lymphocyte precursor (HTLp) frequencies were analyzed in pretransplant and 1 (or 2) and 6-month blood samples taken from liver and lung recipients and were correlated with graft outcome.

RESULTS

In liver allograft recipients with good graft function (n=7), mean donor-specific CTLp frequencies decreased as early as 1 month after transplantation and remained low thereafter. In contrast, mean CTLp frequencies did not decrease in liver allograft recipients with chronic transplant dysfunction (n=6). In lung allograft recipients, donor-specific CTLp frequencies remained relatively high and frequencies were not different between recipients without (n=6) or with (n=6) chronic transplant dysfunction. Donor-specific HTLp frequencies did not change significantly after liver or lung transplantation and did not differ between recipients without or with chronic transplant dysfunction.

CONCLUSIONS

An early decrease in donor-specific CTLp correlates with good graft outcome after liver transplantation. Such rapid decreases in alloreactivity do not occur after lung transplantation illustrating the unique capacity of liver allografts to induce transplantation tolerance.

Soluble HLA class I/CD8 ligation triggers apoptosis in EBV-specific CD8+ cytotoxic T lymphocytes by Fas/Fas-ligand interaction

In the present study, we report that allogeneic soluble HLA class I (sHLA-I) molecules isolated from serum induce apoptosis on EBV-specific CD8(+) Fas(+) cytotoxic T lymphocytes (CTL). CTL apoptosis is induced by the binding of sHLA-I molecules to CD8 and its extent depends on the time of incubation with sHLA-I molecules. Apoptosis is triggered by the interaction of Fas(+) CTL with soluble Fas-ligand, which is released following the binding of sHLA-I antigens to CD8 molecules. These results suggest that sHLA-I molecules may regulate immune responses by inducing apoptosis in virus-specific CTL.

Soluble beta2-mu-associated and beta2-mu-free HLA class I heavy chain serum levels in interferon-alpha nonresponder chronic hepatitis C patients. Markers of immune activation, and response to antiviral retreatment

The serum levels of soluble beta2-mu-associated and beta2-mu-free HLA class I heavy chains were determined in 28 interferon-alpha nonresponder chronic hepatitis C patients retreated with interferon-alpha plus ribavirin and in 70 healthy subjects. The baseline levels of beta2-mu-associated and beta2-mu-free HLA class I heavy chains were significantly higher in patients than in healthy controls (P = 0.001). The levels of beta2-mu-associated HLA class I heavy chains significantly increased in responder patients with respect to nonresponders at the third month of treatment (P = 0.03). At the sixth month of treatment and after 6 months of follow up the levels of beta2-mu-associated HLA class I heavy chains decreased in responder patients and increased in nonresponders. The levels of beta2-mu-free HLA class I heavy chains showed only minor changes during and after treatment. We suggest that the determination of hepatitis C virus RNA levels combined with soluble beta2-mu-associated HLA class I heavy chains, as a marker of immune activation, could identify interferon-alpha non responder chronic hepatitis C patients most likely to respond to a retreatment with interferon-alpha plus ribavirin.

A three-colour flow cytometry technique for measuring trophoblast intracellular antigens: the relative expression of TAP1 in human cytotrophoblast and decidual cells

Flow cytometry is conventionally used to measure cell-surface antigen expression. However, many antigens are found within the cytoplasm, and it is necessary to fix and permeabilize cells to enable antibodies to gain access to them. In this study we have established the conditions for studying intracellular antigens in human trophoblast cells by flow cytometry using an antibody to TAP1 (a key molecule in the process of Class I MHC assembly). We have previously shown by immunocytochemistry that TAP1 expression is apparently greater on Class 1 positive extravillous cytotrophoblast than on any other fetal or maternal tissue. However, as immunohistochemistry is not quantitative we have used three-colour flow cytometry to measure the expression of TAP1 in different trophoblast populations. Villous and extravillous cytotrophoblast were identified in first trimester and term placental and decidual digests on the basis of their expression of cytokeratin and Class I MHC antigens. The level of expression of TAP1 for each population was investigated using a commercial kit that determines the number of antibody-binding sites per cell. TAP expression was found to be three- to fivefold higher in extravillous cytotrophoblast, confirming our previous findings. The techniques developed here are directly applicable to the measurement of other intracellular molecules in trophoblast, in particular cytokines.

Conversion from azathioprine [correction of azathioprina] to mycophenolate mofetil in pediatric renal transplant recipients with chronic rejection

BACKGROUND

Chronic rejection is the leading cause of graft failure. Both nonimmunological and immunological mechanisms contribute to this pathology.

METHODS

We studied changes in kidney function, mixed lymphocyte culture, cell-mediated lympholysis, serum HLA class I antigens, cytotoxic antibodies, and lymphocyte population before and after 6 months of follow-up in 22 pediatric renal transplanted patients. The immunosuppressive protocol used was: cyclosporine, azathioprine, and corticosteroids. Eight patients demonstrated chronic graft rejection (by biopsy), group I; and eight patients had no clinical evidence of chronic and/or acute rejection, group II. Substitution of mycophenolate mofetil (MMF) (600 mg/m2 bid for azathioprine was done in patients of groups I and II. Another six patients with chronic rejection, did not receive MMF, group III.

RESULTS

Creatinine clearance increased in group I (44+/-5 vs. 51.1+/- ml/min/1.73 m2, P<0.03) but it decreased in group III (30+/-3 vs. 25+/-2, P<0.01). Urinary protein excretion decreased only in group I (0.3+/-0.03 to 0.06+/-0.03 g/24 hr, P<0.03). During MMF therapy antidonor mixed lymphocyte culture decreased 62 and 70% (P<0.05) in group I and II. Cell-mediated lympholysis against lymphocyte of the donor decreased 65% (P<0.05) in group I. Cell-mediated lympholysis toward control cells decreased 54% (P<0.01) in group II. Serum HLA class I antigens, only decreased from 0.7+/-0.1 to 0.5+/-0.1 microl/ml, P<0.05, in group I. CD19+ decreased from 7.9+/-1.1 to 5.6+/-0.8%, P<0.05, and 7.8+/-1.2 to 5.5+/-0.9%, P<0.05, in groups I and II, respectively. CD16+ increased from 5.7+/-1.1 to 8.6+/-1.3 (P<0.05) only in group I.

CONCLUSIONS

Our data suggest that substituting MMF for azathioprine therapy leads to an improvement in the immunosuppression and renal function in children with on-going chronic rejection.