IFN-gamma facilitates release of class II-loaded intracellular pools in trophoblast cells: a novel property independent of protein synthesis

The Potential of Soluble Human Leukocyte Antigen Molecules for Early Cancer Detection and Therapeutic Vaccine Design

Human leukocyte antigen (HLA) molecules are essential for anti-tumor immunity, as they display tumor-derived peptides to drive tumor eradication by cytotoxic T lymphocytes. HLA molecules are primarily studied as peptide-loaded complexes on cell membranes (mHLA) and much less attention is given to their secretion as soluble HLA–peptide complexes (sHLA) into bodily fluids. Yet sHLA levels are altered in various pathologies including cancer, and are thus of high interest as biomarkers. Disconcordance in results across studies, however, hampers interpretation and generalization of the relationship between sHLA levels and cancer presence, thereby impairing its use as a biomarker. Furthermore, the question remains to what extent sHLA complexes exert immunomodulatory effects and whether shifts in sHLA levels contribute to disease or are only a consequence of disease. sHLA complexes can also bear tumor-derived peptides and recent advancements in mass spectrometry now permit closer sHLA peptide cargo analysis. sHLA peptide cargo may represent a “liquid biopsy” that could facilitate the use of sHLA for cancer diagnosis and target identification for therapeutic vaccination. This review aims to outline the contradictory and unexplored aspects of sHLA and to provide direction on how the full potential of sHLA as a quantitative and qualitative biomarker can be exploited.

Soluble major histocompatibility complex molecules in immune regulation: highlighting class II antigens

The involvement of major histocompatibility complex (MHC) antigens in the development and regulation of immune response has been well defined over the years, starting from maturation, antigenic peptide loading, migration to the cell membrane for recognition by the T-cell receptor and recycling for immune response cessation. During this intracellular trafficking, MHC antigens find a way to be excreted by the cells, because they can be found as soluble MHC class I (sMHC-I) and class II (sMHC-II) molecules in all body fluids. Although secretion mechanisms have not been sufficiently studied, sMHC molecules have been shown to display important immunoregulatory properties. Their levels in the serum have been shown to be altered in a variety of diseases, including viral infections, inflammation, autoimmunities and cancer, etc. while they seem to be involved in a number of physiological reactions, including maintenance of tolerance, reproduction, as well as mate choice vis-à-vis species evolution. The present review aims to present the thus far existing literature on sMHC molecules and point out the importance of these molecules in the maintenance of immune homeostasis.

Soluble MHC-II proteins promote suppressive activity in CD4+ T cells

Soluble MHCII (sMHCII) molecules are present in body fluids of healthy individuals and are considered to be involved in the maintenance of self tolerance, and are also related to various diseases. Their concentration increases during in vivo antigen-specific tolerogenic stimulation and it was recently shown that exosome-mediated tolerance is MHCII dependent. At the cellular level, sMHCII proteins compete with membrane MHCII for T-cell receptor binding on CD4(+) T cells. Immunoaffinity purification techniques isolated sMHCII antigens from the serum of human serum albumin (HSA) -tolerant mice as a single highly glycosylated protein of ~ 60,000 molecular weight, specifically interacting with anti-class II antibodies in Western blotting and ELISA. Mass spectroscopy showed that these sMHCII proteins were loaded with the tolerogenic peptide as well as multiple self peptides. At the cellular level, sMHCII suppressed antigen-specific, and to a lesser degree antigen-non-specific, spleen cell proliferation and induced CD25 in naive T cells. In T cells activated by antigen-seeded macrophages, sMHCII decreased CD28 and increased CTLA-4 protein expression, while decreasing interleukin-2 and increasing interleukin-10 production. In this case, sMHCII proteins were shown to decrease ZAP-70 and LAT phosphorylation. The results presented here for the first time provide evidence for the role of sMHCII proteins in immune response suppression and maintenance of tolerance, revealing novel regulatory mechanisms for immune system manipulation.

Up regulation of the maternal immune response in the placenta of cattle naturally infected with Neospora caninum

Neospora caninum is an intracellular protozoan parasite which is a major cause of abortion in cattle worldwide. It forms persistent infections which recrudesce during pregnancy leading to foetal infection and in a proportion of cases, abortion. The mechanisms underlying abortion are not understood. In this study, recrudescence of a persistent infection in eight naturally infected cows occurred between 20 and 33 weeks of gestation. Animals were killed at the time of recrudescence and parasites were detected in the placentae and foetuses. An active maternal immune response consisting of an infiltration of CD4+ and CD8+ T cells and a 46–49 fold increase in interferon-γ and interleukin-4 mRNA was detected. Other cytokines, notably interleukin-12 p40, interleukin-10 and tumour necrosis factor-α were also significantly increased and Major Histocompatibility Class II antigen was expressed on maternal and foetal epithelial and stromal fibroblastoid cells. Significantly, despite the presence of an active maternal immune response in the placenta, all the foetuses were alive at the time of maternal euthanasia. There was evidence of parasites within foetal tissues; their distribution was restricted to the central nervous system and skeletal muscle and their presence was associated with tissue necrosis and a non-suppurative inflammatory response involving lymphocytes and macrophages, irrespective of the gestational age of the foetus. Whilst an active maternal immune response to a pathogen in the placenta is generally considered to be damaging to the foetal trophoblast, our findings suggest that the presence of a parasite-induced maternal immune response in the placenta is not detrimental to foetal survival but may contribute to the control of placental parasitosis.

Endogenous versus exogenous fatty acid availability affects lysosomal acidity and MHC class II expression

Although the immune system, inflammation, and cellular metabolism are linked to diseases associated with dyslipidemias, the mechanism(s) remain unclear. To determine whether there is a mechanistic link between lipid availability and inflammation/immune activation, we evaluated macrophage cell lines incubated under conditions of altered exogenous and endogenous lipid availability. Limiting exogenous lipids results in decreased lysosomal acidity and decreased lysosomal enzymatic activity. Both lysosomal parameters are restored with the addition of oleoyl-CoA, suggesting that fatty acids play a role in the regulation of lysosomal function. Cell surface expression of major histocompatibility complex (MHC)-encoded molecules is also decreased in the absence of exogenous lipids. Additionally, we observe decreased gamma-interferon stimulation of cell surface MHC class II. Using cerulenin to limit the endogenous synthesis of fatty acids results in decreased cell surface expression of MHC class II but does not appear to alter lysosomal acidity, suggesting that lysosomal acidity is dependent on exogenous, but not endogenous, fatty acid availability. Testing these conclusions in an in vivo mouse model, we observed statistically significant, diet-dependent differences in lysosomal acidity and MHC class II cell surface expression. Collectively, these data demonstrate a mechanistic link between lipid availability and early events in the immune response.

Constitutive intracellular expression of human leukocyte antigen (HLA)-DO and HLA-DR but not HLA-DM in trophoblast cells

The nonclassic human leukocyte antigen (HLA)-DM molecules have been proved to positively regulate antigen presentation in classic antigen-presenting cells, whereas in B lymphocytes HLA-DO have been identified as negative regulators of the process. The present report examines whether the negative expression of classic class II molecules in trophoblasts implies negative regulation by HLA-DO. It was revealed by immunofluorescence, confocal microscopy, and subcellular fractionation techniques that human trophoblasts, although not expressing any surface HLA-DR antigens, constitutively express intracellular HLA-DR, HLA-DO, and CD74, but not HLA-DM. Administration of interferon-gamma to the cell culture increased HLA-DR and CD74, induced HLA-DM, but did not alter the expression of HLA-DO and induced HLA-DR release from the cells. These results were confirmed by reverse transcriptase-polymerase chain reaction analysis except that HLA-DM mRNA was detected in control cells, indicating a posttranscriptional regulation. Under the same experimental conditions, human monocytes/macrophages were not expressing intracellular HLA-DO while exhibiting significant levels of HLA-DR, HLA-DM, and CD74. The results presented here reveal for the first time expression of HLA-DO in trophoblasts, which can be of great importance in maintaining the class II-negative state in these cells and consequently protecting the fetus from maternal immune attack.

Detection in chick embryo of fetoproteins not recognized by the dam's immune system and of soluble alloantigens. Presumptive teratogenic and abortogenic capacity of their specific IgY

BACKGROUND

The aim of this work was to detect antigens, non-self to the dam, potentially present in chick embryo prior to organogenesis with a view to establishing the consequences of their neutralization on chick development. To this end, hens were immunized with the extract from embryos incubated for 53 h. Their eggs were either used to isolate immunoglobulins for dot and blot tests or incubated for variable lengths of time.

RESULTS

Immunoblot tests, using adsorbed primary and secondary antibodies against paternal serum, revealed the presence of at least four antigens of 32, 34, 70 and 200 kDa that can be classified as soluble alloantigens. The same antibodies against chick embryo extracts (between 53 h and 9) showed at least five aged antigens of 34, 52, 90, 200 and 250 kDa, not detected in cock serum, that can thus be considered as soluble, foreign to the immunized hens and transitory antigens. The abnormalities observed included arrested development and fetal death, as well as minor functional damage in the few chicks that were born alive. The ratio of abnormal to normal embryos was 2.85 in the experimental group and 0.43 in the control group. With regard to congenital anomalies it must be said that of the 81 eggs incubated only four chicks were born alive, and of these, only one had a healthy birth and subsequent growth. The other three showed a transitory ataxia and one of them presented adult lumbar scoliosis and asymmetric pelvis.

CONCLUSIONS

The problem of recurrent spontaneous abortions is revisited in the light of these results. Some recent data suggest that soluble alloantigens may be candidates for a new etiological entity in recurrent spontaneous abortions. They can also be the cause of some congenital anomalies. The soluble, foreign, transitory antigens may have a similar effect although there is no supportive data in the literature.

Mutation analysis of BrCA1, BrCA2, and p53 versus soluble HLA class I and class II in a case of familial endometriosis

OBJECTIVE

To investigate possible correlation(s) between mutations of BrCA1, BrCA2, and p53 genes versus soluble HLA expression in familial endometriosis.

DESIGN

Mutation analysis.

SETTING

University teaching departments and hospital.

PATIENT(S)

A family with seven women in two generations with familial endometriosis.

INTERVENTION(S)

Mutation analysis of BrCA1, BrCA2, and p53 genes.

MAIN OUTCOME MEASURE(S)

A point mutation of the BrCA1 gene appears to inhibit soluble HLA secretion.

RESULT(S)

Among the three genes examined, only the BrCA1 gene showed a T to A mutation at position 3232 that correlates with total abolishment of both class I and class II antigen release.

CONCLUSION(S)

A possible correlation between a BrCA1 mutation and soluble HLA expression appears to exist. The mutation is not stage dependent and seemingly influences the secretion of both class I and class II antigens that are totally absent from the serum of only one family member.

The possible anti-inflammatory role of circulating human leukocyte antigen levels in women with endometriosis after treatment with danazol and leuprorelin acetate depot

BACKGROUND

Endometriosis is defined as an inflammatory condition of the female reproductive tract, a state often associated with infertility and miscarriage. Many exogenously administered factors (treatments) control the disease via as yet unknown pathways. Possible candidate molecules involved in these mechanisms could be the serum-soluble human leukocyte antigens (sHIA) that have been detected in a variety of human body fluids and that are associated with several diseases.

AIMS

We here examine how danazol and leuprorelin acetate depot treatments exert their anti-inflammatory action. It is plausible that subtle alterations mediated by these treatments and in relation to sHLA may explain the pathophysiology of endometriosis and provide insights towards new therapeutic protocols.

METHODS

Indirect enzyme-linked immunosorbent assay (ELISA), using specific monoclonal antibodies, determined serum-soluble class-I and class-II HLA levels. ELISA readings from treated women were compared with normal healthy subjects.

RESULTS

Serum-soluble class-I and class-II HLA levels are statistically significantly lower (P < 0.001) in women with endometriosis than in the control groups. However, danazol but not leuprorelin acetate depot administration augments soluble HLA class I and class II (P < 0.01 and P < 0.001, respectively) to normal levels during the treatment period, an increase that may account for the anti-inflammatory effect and the remission observed.

CONCLUSIONS

It is shown that one of the underlying causes of endometriosis may be the lack of both circulating class-I and class-II antigen levels. Danazol administration acts via an induced release of these antigens, whose presence correlates with the degree of the inflammatory alleviation obtained. We thus provide evidence that the inflammatory state of the disease appears to be associated with soluble HLA levels because, 3 months after ceasing therapy, the circulating antigens in the serum return to the same levels that correspond to the pathological condition.