Immune-privileged Site Research Articles

Donor-antigen Inoculation in the Testis Promotes Skin Allograft Acceptance Induced by Conventional Costimulatory Blockade via Induction of CD8 + CD122+ and CD4 + CD25+ Regulatory T Cells.

Immune responses are somewhat suppressed in immune privileged sites, including the testes, which provide a preexisting opportunity to prolong allograft survival. Previous studies have shown that intratesticular islet allografts enjoy extended survival even without any immunosuppression. However, it is unknown if testicular immune privilege can be exploited to prolong the survival of a solid allograft, including the skin, because it is impractical to implant a solid tissue in human testes. To immunize recipient mice, splenocytes from BALB/c mice were injected into the testis of C57BL/6 recipients 1 week before skin transplantation. CD8 + CD122+ and CD4 + FoxP3+ regulatory T [Treg] cells were quantified by fluorescence-activated cell sorting. Although donor-antigen inoculation alone did not delay skin allograft rejection, it significantly extended the allograft survival when combined with CD40/CD40L or B7/CD28 costimulatory blockade and further induced long-term skin allograft acceptance when both costimulatory pathways were blocked. Similarly, donor-antigen inoculation suppressed alloreactive T cell proliferation in draining lymph nodes of skin recipients in the presence of the same costimulatory blockade. Interestingly, donor-antigen inoculation via intratesticular injection increased CD8 + CD122+, but not CD4 + FoxP3+, Treg numbers after transplantation. However, both CD8 + CD122+ and CD4 + CD25+ Treg cells induced by donor-antigen inoculation and the costimulatory blockade were more potent in suppression than that induced without the inoculation. Depletion of CD8+ or CD25+ T cells largely abrogated long-term skin allograft survival induced by donor-antigen inoculation and the costimulatory blockade. Intratesticular inoculation with donor antigens promotes long-term skin allograft survival induced by conventional costimulatory blockade via the induction of both CD8 + CD122+ and CD4 + CD25+ Treg cells.

Clinical perspectives of TRAIL: insights into central nervous system disorders.

The TNF-related apoptosis inducing ligand TRAIL is a member of the TNF superfamily that has been firstly studied and evaluated for its anti-cancer activity, and the insights into its biology have already led to the identification of several TRAIL-based anticancer strategies with strong clinical therapeutic potentials. Nonetheless, the TRAIL system is far more complex and it can lead to a wider range of biological effects other than the ability of inducing apoptosis in cancer cells. By virtue of the different receptors and the different signalling pathways involved, TRAIL plays indeed a role in the regulation of different processes of the innate and adaptive immune system and this feature makes it an intriguing molecule under consideration in the development/progression/treatment of several immunological disorders. In this context, central nervous system represents a peculiar anatomic site where, despite its “status” of immune-privileged site, both innate and adaptive inflammatory responses occur and are involved in several pathological conditions. A number of studies have evaluated the role of TRAIL and of TRAIL-related pathways as pro-inflammatory or protective stimuli, depending on the specific pathological condition, confirming a twofold nature of this molecule. In this light, the aim of this review is to summarize the main preclinical evidences of the potential/involvement of TRAIL molecule and TRAIL pathways for the treatment of central nervous system disorders and the key suggestions coming from their assessment in preclinical models as proof of concept for future clinical studies.

Isolation of Sertoli Cells and Peritubular Cells from Rat Testes.

The testis, and in particular the male gamete, challenges the immune system in a unique way because differentiated sperm first appear at the time of puberty - more than ten years after the establishment of systemic immune tolerance. Spermatogenic cells express a number of proteins that may be seen as non-self by the immune system. The testis must then be able to establish tolerance to these neo-antigens on the one hand but still be able to protect itself from infections and tumor development on the other hand. Therefore the testis is one of a few immune privileged sites in the body that tolerate foreign antigens without evoking a detrimental inflammatory immune response. Sertoli cells play a key role for the maintenance of this immune privileged environment of the testis and also prolong survival of cotransplanted cells in a foreign environment. Therefore primary Sertoli cells are an important tool for studying the immune privilege of the testis that cannot be easily replaced by established cell lines or other cellular models. Here we present a detailed and comprehensive protocol for the isolation of Sertoli cells - and peritubular cells if desired - from rat testes within a single day.

Novel Insights into the Role of Defensins in Virus-Induced Autoimmunity in the Central Nervous System

Virus-induced autoimmunity in the brain, an immune-privileged site, occurs primarily from a breach in thymic selection mechanisms that constitute peripheral tolerance, culminating in a self-directed, Tcell- mediated immune response traditionally thought to occur via molecular or epitope mimicry; immune recognition of novel selfantigens; bystander activation of autoreactive defensin-specific, Tlymphocytes (ATLs); and aberrant expression of cytokines in polyclonically expanded T-cell subsets.

The Evaluation of Cancer Testis Gene PIWIL2 Expression Levels as a New Prognostic Biomarker for Breast Cancer.

Breast cancer is the most prevalent cancer and foremost reason of death resulting from malignancy among women worldwide. In recent years, it has been reported that a group of genes named cancer testis genes (CTg) express in adult immune privileged sites and some embryonic tissues. Likewise, it has been demonstrated that CTgs express aberrantly in various tumors and play essential roles in both initiation and development of cancers. In this study, PIWIL2, one member of CTgs, which has an indispensable role in spermatogenesis and tumorigenesis, was examined as an efficient prognostic and diagnostic biomarker in breast cancer. It is worth mentioning that the expression study of PIWIL2 by qPCR on breast cancer samples was performed for the first time, since this approach is much more sensitive than western blot, RT-PCR, and immunohistochemistry. To investigate the expression status of PIWIL2 in breast cancer, 72 fresh cancerous and normal adjacent specimens from 44 patients who had undergone surgery in Shahid Faghihi Hospital were used. None of the patients had received chemotherapy. The relationships between the PIWIL2 status and the clinicopathological parameters were ultimately determined. It was ascertained that the expression rates of PIWIL2 in cancerous breast tissues were related to patients' age, tumor stage, tumor size, tumor grade, and lymph node involvement (p < 0.05). The PIWIL2 gene could be considered as an efficient prognostic biomarker in breast cancer.

Brain-derived neurotrophic factor in patients with advanced age-related macular degeneration.

To investigate the serum level of the brain-derived neurotrophic factor (BDNF) in age-related macular degeneration (AMD) and healthy control subjects. The disruption in the tight balance of neuroinflammatory and neuroprotective processes in an immune-privileged site like retina is proposed to contribute to the pathogenesis of AMD. One of the main neuroprotective mediators in the central nervous system is BDNF with its serum level notably affected in several neurodegenerative disorders. Thirty-six patients with AMD and 36 age-matched controls were enrolled in this study. The serum level of BDNF was measured using the enzyme-linked immunosorbent assay method. Results were analyzed to compare case and control values. Comparisons were also made between the BDNF level of wet- vs dry-AMD, and male vs female patients and controls. Analysis of variance (ANOVA) and Student's t-test were employed to analyze the data. The mean BDNF levels in AMD group were significantly higher than the control group. Furthermore, our analysis revealed greater BDNF values in all AMD subgroups compared to controls (P=0.004, 0.005, 0.001 and 0.02 for male wet-AMD, male dry-AMD, female wet-AMD and female dry-AMD vs controls, respectively). The BDNF level however did not vary between wet- and dry-AMD patients (P=0.74). While within-group comparisons in males and females of AMD and control groups did not show any difference in BDNF (P=0.16, 0.64 and 0.85 for wet-AMD, dry-AMD and control groups, respectively), between-group data showed a higher mean BDNF in both male and female AMD subjects than their peer controls. This study demonstrated that the serum BDNF level is different in patients with AMD as compared to subjects without AMD. Future attempts should be done to unravel beneficial or deleterious effect of this neurotrophin in the pathogenesis of AMD.

Immunotherapy in Multiple Myeloma Using Cancer-Testis Antigens.

Context:Multiple myeloma (MM) is a B-cell malignancy characterized by monoclonal expansion of abnormal plasma cells in the bone marrow. It accounts for 10% of hematological malignancies. Although patients respond to a wide range of anticancer modalities, relapse occurs in a significant number of the cases. Immunotherapeutic approaches have been evolved to tackle this problem. Cancer-testis antigens CTAs as a group of tumor-associated antigens are appropriate targets for cancer immunotherapy as they have restricted expression pattern in normal tissues except for testis which is an immune-privileged site. Expression of these antigens has been assessed in different malignancies including MM.Evidence Acquisition:We performed a computerized search of the MEDLINE/PubMed databases with key words: multiple myeloma, cancer-testis antigen, and cancer stem cell and immunotherapy.Results:Several CTAs including NY-ESO-1, MAGE and GAGE family have been shown to be expressed in MM patients. Cellular and humoral immune responses against these antigens have been detected in MM patients.Conclusions:The frequent and high expression level of CTAs in MM patients shows that these antigens can be applied as cancer biomarkers as well as targets for immunotherapy in these patients.

Ocular surgical models for immune and angiogenic responses.

Corneal transplantation serves as a reproducible and simple surgical model to study mechanisms regulating immunity and angiogenesis. The simplicity of the model allows for systematic analysis of different mechanisms involved in immune and angiogenic privilege and their failures. This protocol describes how to induce neovessels and inflammation in an actively regulated avascular and immune-privileged site. This involves placing intra-stromal corneal sutures for two weeks, disrupting the privileges, and performing corneal transplantation subsequently. Privileged and non-privileged recipient responses to donor cornea can be compared to identify key immunological mechanisms that underlie angiogenesis and graft rejection. This protocol can also be adapted to the growing repertoire of genetic models available in the mouse, and is a valuable tool to elucidate molecular mechanisms mediating acceptance or failure of corneal graft. The model could be used to assess the potential of therapeutic molecules to enhance graft survival in vivo.

Neural immune modulation and immunotherapy assisted by focused ultrasound induced blood-brain barrier opening

The central nervous system (CNS) has long been regarded as an immune-privileged site, with the blood-brain barrier (BBB) limiting the entering of systemic immune cells and components. Exposure of low-energy focused ultrasound (FUS) with the presence of microbubbles has been found to provide a temporary and targeted opening of the BBB without inflicting brain damage or inflammation, and is thus an attractive means of delivering CNS therapeutic agents and raising the potential for targeted CNS immunotherapy. Based on our recent studies on enhancing brain-tumor immune-related therapy via this mechanism,1 we summarize current approaches using FUS-induced BBB opening to promote immune regulation and project potential directions for FUS-induced CNS immunotherapy.

The immune response of stem cells in subretinal transplantation.

Stem cell transplantation is a potential curative treatment for degenerative diseases of the retina. Among cell injection sites, the subretinal space (SRS) is particularly advantageous as it is maintained as an immune privileged site by the retinal pigment epithelium (RPE) layer. Thus, the success of subretinal transplantation depends on maintenance of RPE integrity. Moreover, both embryonic stem cells (ESCs) and mesenchymal stem cells (MSCs) have negligible immunogenicity and in fact are immunosuppressive. Indeed, many studies have demonstrated that immunosuppressive drugs are not necessary for subretinal transplantation of stem cells if the blood-retinal barrier is not breached during surgery. The immunogenicity of induced pluripotent stem cells (iPSCs) appears more complex, and requires careful study before clinical application. Despite low rates of graft rejection in animal models, survival rates for ESCs, MSCs, and iPSCs in retina are generally poor, possibly due to resident microglia activated by cell transplantation. To improve graft survival in SRS transplantation, damage to the blood-retinal barrier must be minimized using appropriate surgical techniques. In addition, agents that inhibit microglial activation may be required. Finally, immunosuppressants may be required, at least temporarily, until the blood-retinal barrier heals. We review surgical methods and drug regimens to enhance the likelihood of graft survival after SRS transplantation.

Dual roles of endogenous and exogenous galectin-1 in the control of testicular immunopathology.

Galectin-1 (Gal-1), a proto-type member of galectin family, is highly expressed in immune privileged sites, including the testis. However, in spite of considerable progress the relevance of endogenous and exogenous Gal-1 in testis pathophysiology have not yet been explored. Here we evaluated the in vivo roles of Gal-1 in experimental autoimmune orchitis (EAO), a well-established model of autoimmune testicular inflammation associated with subfertility and infertility. A significant reduction in the incidence and severity of EAO was observed in mice genetically deficient in Gal-1 (Lgals1−/−) versus wild-type (WT) mice. Testicular histopathology revealed the presence of multifocal testicular damage in WT mice characterized by an interstitial mononuclear cell infiltrate and different degrees of germ cell sloughing of seminiferous tubules. TUNEL assay and assessment of active caspase-3 expression, revealed the prevalence of apoptotic spermatocytes mainly localized in the adluminal compartment of seminiferous tubules in EAO mice. A significant increased number of TUNEL-positive germ cells was detected in EAO testis from WT compared with Lgals1−/− mice. In contrast, exogenous administration of recombinant Gal-1 to WT mice undergoing EAO attenuated the severity of the disease. Our results unveil a dual role of endogenous versus exogenous Gal-1 in the control of autoimmune testis inflammation.

High frequency of MYD88 mutations in vitreoretinal B-cell lymphoma: a valuable tool to improve diagnostic yield of vitreous aspirates

AbstractVitreoretinal diffuse large B-cell lymphoma is a rare disorder, occurring as primary ocular disease or as secondary involvement by primary central nervous system lymphoma. It is usually diagnosed by cytologic, immunocytochemical, and molecular examination of vitreous aspirates. However, distinguishing vitreoretinal diffuse large B-cell lymphoma from uveitis remains difficult, and clonality analysis may be either unsuccessful or misleading. Diffuse large B-cell lymphoma arising in immune-privileged sites (eg, the central nervous system) shows a high frequency of MYD88 mutations. Therefore, we retrospectively assessed the frequency of MYD88 mutations in vitreoretinal lymphoma (VRL) and their diagnostic potential in 75 vitrectomy samples of 69 patients, and validated our results in a separate cohort (n = 21). MYD88 mutations were identified in 20 of 29 (69%) clinically, histologically, and molecularly confirmed VRL, including 6 cases of the test cohort initially diagnosed as reactive (3/6) or suspicious (3/6) for lymphoma. MYD88 mutations, especially L265P, are very frequent in VRL and their detection significantly improves the diagnostic yield of vitrectomy specimens.

Transcription of non-classic major histocompatibility complex (MHC) class I in the bovine placenta throughout gestation and after Brucella abortus infection

Transcription of non-classical major histocompatibility complex class I (MHC-I) was assessed in the bovine placenta throughout gestation. Additionally, the effect of Brucella abortus infection on expression of non-classical MHC-I was also evaluated using a chorioallantoic membrane explant model of infection. The non-classical MHC-I genes MICB and NC3 had higher levels of transcription in the intercotyledonary region when compared to the placentome, which had higher levels of transcription at the second trimester of gestation. NC1 and classical MHC-I had very low levels of transcription throughout gestation. Trophoblastic cells of B. abortus-infected chorioallantoic membrane explants had an increase in transcription of non-classical MHC-I at 4h post infection. Therefore, this study provides an analysis of non-classical MHC-I transcription at different stages of gestation and different placental tissues, and during B. abortus infection. These findings provide additional knowledge on immune regulation in placental tissues, a known immune-privileged site.

Cartilage immunoprivilege depends on donor source and lesion location

The ability to repair damaged cartilage is a major goal of musculoskeletal tissue engineering. Allogeneic (same species, different individual) or xenogeneic (different species) sources can provide an attractive source of chondrocytes for cartilage tissue engineering, since autologous (same individual) cells are scarce. Immune rejection of non-autologous hyaline articular cartilage has seldom been considered due to the popular notion of “cartilage immunoprivilege”. The objective of this study was to determine the suitability of allogeneic and xenogeneic engineered neocartilage tissue for cartilage repair. To address this, scaffold-free tissue engineered articular cartilage of syngeneic (same genetic background), allogeneic, and xenogeneic origin were implanted into two different locations of the rabbit knee (n=3 per group/location). Xenogeneic engineered cartilage and control xenogeneic chondral explants provoked profound innate inflammatory and adaptive cellular responses, regardless of transplant location. Cytological quantification of immune cells showed that, while allogeneic neocartilage elicited an immune response in the patella, negligible responses were observed when implanted into the trochlea; instead the responses were comparable to microfracture-treated empty defect controls. Allogeneic neocartilage survived within the trochlea implant site and demonstrated graft integration into the underlying bone. In conclusion, the knee joint cartilage does not represent an immune privileged site, strongly rejecting xenogeneic but not allogeneic chondrocytes in a location-dependent fashion. This difference in location-dependent survival of allogeneic tissue may be associated with proximity to the synovium. Statement of SignificanceThrough a series of in vivo studies this research demonstrates that articular cartilage is not fully immunoprivileged. In addition, we now show that anatomical location of the defect, even within the same joint compartment, strongly influences the degree of the resultant immune response. This is one of the first investigations to show that (1) immune tolerance to allogeneic tissue engineered cartilage and (2) subsequent implant survival are dependent on the implant location and proximity to the synovium.

Stem Cell Therapies for Intervertebral Disc Degeneration: Immune Privilege Reinforcement by Fas/FasL Regulating Machinery.

As a main contributing factor to low back pain, intervertebral disc degeneration (IDD) is the fundamental basis for various debilitating spinal diseases. The pros and cons of current treatment modalities necessitate biological treatment strategies targeting for reversing or altering the degeneration process in terms of molecules or genes. The advances in stem cell research facilitate the studies aiming for possible clinical application of stem cell therapies for IDD. Human NP cells are versatile with cell morphology full of variety, capable of synthesizing extracellular matrix components, engulfing substances by autophagy and phagocytosis, mitochondrial vacuolization indicating dysfunction, expressing Fas and FasL as significant omens of immune privileged sites. Human discs belong to immune privilege organs with functional FasL expression, which can interact with invasive immune cells by Fas-FasL regulatory machinery. IDD is characterized by decreased expression level of FasL with dysfunctional FasL, which in turn unbalances the interaction between NP cells and immune cells. Certain modulation factors might play a role in the process, such as miR-155. Accumulating evidence indicates that Fas-FasL network expresses in a variety of stem cells. Given the expression of functional FasL and insensitive Fas in stem cells (we term as FasL privilege), transplantation of stem cells into the disc may regenerate the degenerative disc by not only differentiating into NP-like cells, increasing extracellular matrix, but also reinforce immune privilege via interaction with immune cells by Fas-FasL network.

Anti-NR2A/B Antibodies and Other Major Molecular Mechanisms in the Pathogenesis of Cognitive Dysfunction in Systemic Lupus Erythematosus.

Systemic lupus erythematosus (SLE) is an autoimmune disease that affects approximately 1–45.3 per 100,000 people worldwide. Although deaths as a result of active and renal diseases have been substantially declining amongst SLE patients, disease involving the central nervous system (CNS), collectively termed neuropsychiatric systemic lupus erythematosus (NPSLE), remains one of the important causes of death in these patients. Cognitive dysfunction is one of the most common manifestations of NPSLE, which comprises deficits in information-processing speed, attention and executive function, in conjunction with preservation of speech. Albeit a prevalent manifestation of NPSLE, the pathogenetic mechanisms of cognitive dysfunction remain unclear. Recent advances in genetic studies, molecular techniques, neuropathology, neuroimaging and cognitive science have gleaned valuable insights into the pathophysiology of lupus-related cognitive dysfunction. In recent years, a role for autoantibodies, molecular and cellular mechanisms in cognitive dysfunction, has been emerging, challenging our previous concept of the brain as an immune privileged site. This review will focus on the potential pathogenic factors involved in NPSLE, including anti-N-methyl-d-aspartate receptor subunit NR2A/B (anti-NR2A/B) antibodies, matrix metalloproteinase-9, neutrophil extracellular traps and pro-inflammatory mediators. Better understanding of these mechanistic processes will enhance identification of new therapeutic modalities to halt the progression of cognitive decline in SLE patients.

Immunization with donor splenocytes in testis of recipient mice promotes induction of long-term survival of islet allografts transplanted in a conventional site (TRAN1P.920)

Abstract Immune responses are subdued in immune privileged sites, which provide a unique opportunity to prolong cellular allograft survival. We and others have previously shown that inducing tolerance of islet allografts transplanted in murine testes is easier than in conventional sites. However, it is not practical to transplant islets in human testes. Here we found that immunization of B6 recipients with irradiated Balb/C splenocytes through testicular injection, 7 and 14 days before islet transplantation under the kidney capsule, promotes long-term allograft survival induced by low doses of anti-CD40L (MR1) or CTLA4-Ig (0.1mg/day, days 0,2,4,6), with 75% islet allografts achieving long-term survival (&amp;gt;120 days). Same Ab treatment without the immunization failed to do so. Immunization without MR1 or CTLA4-Ig did not prolong allograft survival. We also found that islet transplantation under renal capsule of previously immunized recipients generates much less CD44+CD8+ memory T cells but induces more CD4+CD25+ Tregs than under renal capsule of unimmunized recipients. These Tregs exhibited donor-specific suppression of alloimmune responses in vitro. These findings reveal new mechanisms of immune privilege and may provide novel approaches to inducing long-term allograft survival or transplant tolerance in both immunologically privileged and unprivileged sites.

Regulation of indoleamine 2,3-dioxygenase in primary human saphenous vein endothelial cells.

BackgroundIndoleamine 2,3-dioxygenase (IDO) is an enzyme associated with the regulation of immune responses. Cytokines such as IFNγ induce its expression in endothelial cells originating from immune-privileged sites. In this study, we investigate regulators of IDO in primary endothelial cells from a non-immune-privileged site and determine whether IDO expression affects immune cell behavior.MethodsIDO expression was determined using real-time quantitative polymerase chain reaction and immunoblotting. IDO activity was estimated using an IDO enzyme assay. Primary cells were transfected using microporation, and T-cell migration was determined using a cell transmigration assay.ResultsIDO is expressed in human saphenous vein endothelial cells after stimulation with IFNγ but not after treatment with TNFα, IL-1β, IL-2, IL-4, IL-6, or IL-10. VEGFβ and heparin negatively regulate IFNγ-driven increases in IDO. Overexpression of IDO in endothelial cells does not affect transmigration of T-cells.ConclusionIDO is expressed in human saphenous vein endothelial cells after stimulation with IFNγ. Heparin and angiogenesis stimulators such as VEGFβ negatively regulate its expression.

Exclusion of T Cells From Pancreatic Carcinomas in Mice Is Regulated by Ly6Clow F4/80+ Extratumoral Macrophages

Immunotherapies that induce T-cell responses have shown efficacy against some solid malignancies in patients and mice, but these have little effect on pancreatic ductal adenocarcinoma (PDAC). We investigated whether the ability of PDAC to evade T-cell responses induced by immunotherapies results from the low level of immunogenicity of tumor cells, the tumor's immunosuppressive mechanisms, or both. Kras(G12D/+);Trp53(R172H/+);Pdx-1-Cre (KPC) mice, which develop spontaneous PDAC, or their littermates (controls) were given subcutaneous injections of a syngeneic KPC-derived PDAC cell line. Mice were then given gemcitabine and an agonist of CD40 to induce tumor-specific immunity mediated by T cells. Some mice were also given clodronate-encapsulated liposomes to deplete macrophages. Tumor growth was monitored. Tumor and spleen tissues were collected and analyzed by histology, flow cytometry, and immunohistochemistry. Gemcitabine in combination with a CD40 agonist induced T-cell-dependent regression of subcutaneous PDAC in KPC and control mice. In KPC mice given gemcitabine and a CD40 agonist, CD4(+) and CD8(+) T cells infiltrated subcutaneous tumors, but only CD4(+) T cells infiltrated spontaneous pancreatic tumors (not CD8(+) T cells). In mice depleted of Ly6C(low) F4/80(+) extratumoral macrophages, the combination of gemcitabine and a CD40 agonist stimulated infiltration of spontaneous tumors by CD8(+) T cells and induced tumor regression, mediated by CD8(+) T cells. Ly6C(low) F4/80(+) macrophages that reside outside of the tumor microenvironment regulate infiltration of T cells into PDAC and establish a site of immune privilege. Strategies to reverse the immune privilege of PDAC, which is regulated by extratumoral macrophages, might increase the efficacy of T-cell immunotherapy for patients with PDAC.

Relation Between HLA-G Gene Null Allele (HLA-G*0105N) and Recurrent Miscarriage

: Human leukocyte antigen-G (HLA-G) is a nonclassical HLA-class I antigen located on chromosome 6. HLA-G is highly expressed on cytotrophoblast cells at the fetomaternal interface and involved in the development of pregnant uterus as an immune privileged site. Expression of HLA-G is thought to have a critical role in the protection of the semiallogenic fetus from maternal immune attack during pregnancy. HLA-G molecules bind inhibitory receptors on maternal T cells and NK cells and subsequently inhibit their cytolytic activities. Because of mRNA alternative splicing of HLA-G primary transcript, the HLA-G protein exists in both membrane-bound (HLA-G1 to G4) and soluble (HLA-G5 to G7) isoforms. HLA-G gene contains 15 alleles, including the HLA-G*0105N null allele. A single base-pair deletion of a cytosine (1597delC) results in open reading frame mutation, which leads to a premature stop codon. The HLA-G*0105N allele is unable to generate the HLA-G1, HLA-G5, and HLA-G4 isoforms. However, it is still able to produce other HLA-G proteins, in which exon 3 is removed by alternative splicing, including HLA-G2, G3, G6 and G7 isoforms. HLA-G*0105N null allele has been described in healthy adults with successful and normal pregnancies, which suggests that HLA-G function is not restricted to the HLA-G1 isoform. Description of healthy individual homozygous for HLA-G*0105N allele recommends that truncated HLA-G2 and G3 isoforms encoded by null allele are able to compensate for the lack of the HLA-G1, G4 and G5 isoforms. Results of the numerous studies on the null allele of HLA-G gene indicated that its selection may have increased the frequency of the HLA-G*0105N. Studies on the null allele of HLA-G gene could be useful in determining the frequency of genetic variants of HLA-G alleles in different ethnic groups.