Cell-mediated immunity to Epstein-Barr virus (EBV) and natural killer (NK)-cell activity in the X-linked lymphoproliferative syndrome

A case of adult-onset X-linked lymphoproliferative disease mimicking pulmonary infection

X-linked lymphoproliferative disease (XLP) is a rare primary immunodeficiency with susceptibility and vulnerability to Epstein-Barr virus (EBV) infection. Most patients were diagnosed in early childhood and do not survive into adulthood. Here we reported an adult-onset XLP patient presenting with fever, dyspnea, and pulmonary nodules, mimicking respiratory infection at disease onset. Diagnosis was made based on whole-exon sequencing and pedigree analysis. Chest CT showed bilateral nodular lesions partially responsive to steroid therapy. The symptoms were managed with high-dose steroid, together with broad-spectrum anti-infective treatment for mixed secondary opportunistic infections. Pathology studies revealed non-Langerhans histiocytosis and T cell infiltration in lungs. Our case highlights the importance of genetic sequencing in managing young patients with unexplained infection and potential immuno-deficiency. We also added to the understanding of XLP by carrying detailed investigation into the pulmonary lesions.

Allosteric inhibition of SHP2 rescues functional T-cell abnormalities in SAP deficiency

BACKGROUND

X-linked lymphoproliferative disease (XLP) is a primary immunodeficiency arising from SH2D1A mutations leading to loss of SLAM-associated protein (SAP). SAP is an intracellular adaptor protein that binds to SLAM family receptors and is expressed in specific lymphoid lineages. In T cells, SAP relays activatory signals from the T-cell receptor but in its absence SH2 containing protein tyrosine phosphase-1 (SHP1), SH2 containing protein tyrosine phosphase-2 (SHP2), and SH2 containing inositol 5'-phosphatase proteins (SHIP) induce T-cell inhibitory signals leading to abnormal T-cell responses. This results in severe clinical manifestations including immune dysregulation, dysgammaglobulinemia, lymphoma, and hemophagocytic lymphohistiocytosis. Current treatment relies on supportive therapies including immunoglobulin replacement and symptom-directed therapy, with hematopoietic stem cell transplant offering the only curative option.

OBJECTIVES

As most XLP symptoms are due to defective T-cell function, this study investigated whether inhibition of SHP2 can restore cellular function in the absence of SAP.

METHODS

Healthy donor and XLP patient T cells were activated with anti-CD3/CD28 in T-cell media supplemented with a SHP2 inhibitor (RMC-4550 in vitro for 24 hours) and functional assays were performed to assess follicular T_H (T_FH) cell function, CD8 cytotoxicity, and sensitivity to restimulation-induced cell death. Additionally, SAP-deficient (SAP^y/-) mice were treated with RMC-4550 before T-cell mediated challenge with 4-hydroxy-3-nitrophenylacetly conjugated chicken gammaglobulin and subsequent assessment of humoral immunity analyzing T_FH cell population, germinal center formation, and antigen-dependent immunoglobulin secretion.

RESULTS

This study shows that the use of RMC-4550 restores T-cell function in XLP patient cells and a SAP^y/- model, demonstrating restoration of T_FH cell function through immunoglobulin and cytokine secretion analysis alongside rescue of cytotoxicity and restimulation-induced cell death.

CONCLUSIONS

These data suggest that SHP2 inhibitors could offer a novel and effective targeted treatment approach for patients with XLP.

Inherited Immunodeficiencies With High Predisposition to Epstein-Barr Virus-Driven Lymphoproliferative Diseases

Epstein–Barr Virus (EBV) is a gamma-herpes virus that infects 90% of humans without any symptoms in most cases, but has an oncogenic potential, especially in immunocompromised individuals. In the past 30 years, several primary immunodeficiencies (PIDs) associated with a high risk to develop EBV-associated lymphoproliferative disorders (LPDs), essentially consisting of virus-associated hemophagocytic syndrome, non-malignant and malignant B-cell LPDs including non-Hodgkin and Hodgkin’s types of B lymphomas have been characterized. Among them are SH2D1A (SAP), XIAP, ITK, MAGT1, CD27, CD70, CTPS1, RASGRP1, and CORO1A deficiencies. Penetrance of EBV infection ranges from 50 to 100% in those PIDs. Description of large cohorts and case reports has refined the specific phenotypes associated with these PIDs helping to the diagnosis. Specific pathways required for protective immunity to EBV have emerged from studies of these PIDs. SLAM-associated protein-dependent SLAM receptors and MAGT1-dependent NKG2D pathways are important for T and NK-cell cytotoxicity toward EBV-infected B-cells, while CD27–CD70 interactions are critical to drive the expansion of EBV-specific T-cells. CTPS1 and RASGRP1 deficiencies further strengthen that T-lymphocyte expansion is a key step in the immune response to EBV. These pathways appear to be also important for the anti-tumoral immune surveillance of abnormal B cells. Monogenic PIDs should be thus considered in case of any EBV-associated LPDs.

X-Linked Lymphoproliferative Disease Type 1: A Clinical and Molecular Perspective

X-linked lymphoproliferative disease (XLP) was first described in the 1970s as a fatal lymphoproliferative syndrome associated with infection with Epstein–Barr virus (EBV). Features include hemophagocytic lymphohistiocytosis (HLH), lymphomas, and dysgammaglobulinemias. Molecular cloning of the causative gene, SH2D1A, has provided insight into the nature of disease, as well as helped characterize multiple features of normal immune cell function. Although XLP type 1 (XLP1) provides an example of a primary immunodeficiency in which patients have problems clearing primarily one infectious agent, it is clear that XLP1 is also a disease of severe immune dysregulation, even independent of EBV infection. Here, we describe clinical features of XLP1, how molecular and biological studies of the gene product, SAP, and the associated signaling lymphocyte activation molecule family receptors have provided insight into disease pathogenesis including specific immune cell defects, and current therapeutic approaches including the potential use of gene therapy. Together, these studies have helped change the outcome of this once almost uniformly fatal disease.

XLP: clinical features and molecular etiology due to mutations in SH2D1A encoding SAP

X-linked lymphoproliferative disease (XLP) is a rare primary immunodeficiency affecting approximately 1-2 per 1 million males. A key feature of XLP is the exquisite sensitivity of affected individuals to disease induced following EBV infection. However, patients can also develop hypogammaglobulinemia and B-cell lymphoma independently of exposure to EBV. XLP is caused by loss-of function mutations in SH2D1A, which encodes the intracellular adaptor molecule SAP. SAP is predominantly expressed in T cells and NK cells, and functions to regulate signal transduction pathways downstream of the SLAM family of surface receptors to control CD4+ T cell (and by extension B cells), CD8+ T cell and NK cell function, as well as the development of NKT cells. The study of XLP had shed substantial light on the requirements for lymphocyte differentiation and immune regulation, which in turn have the potential to be translated into novel treatments for not only XLP patients but individuals affected by EBV-induced disease, impaired humoral immunity and malignancy.

Fine specificity and molecular competition in SLAM family receptor signalling

SLAM family receptors regulate activation and inhibition in immunity through recruitment of activating and inhibitory SH2 domain containing proteins to immunoreceptor tyrosine based switch motifs (ITSMs). Binding of the adaptors, SAP and EAT-2 to ITSMs in the cytoplasmic regions of SLAM family receptors is important for activation. We analysed the fine specificity of SLAM family receptor phosphorylated ITSMs and the conserved tyrosine motif in EAT-2 for SH2 domain containing signalling proteins. Consistent with the literature describing dependence of CRACC (SLAMF7) on EAT-2, CRACC bound EAT-2 (K_D = 0.003 μM) with approximately 2 orders of magnitude greater affinity than SAP (K_D = 0.44 μM). RNA interference in cytotoxicity assays in NK92 cells showed dependence of CRACC on SAP in addition to EAT-2, indicating selectivity of SAP and EAT-2 may depend on the relative concentrations of the two adaptors. The concentration of SAP was four fold higher than EAT-2 in NK92 cells. Compared with SAP, the significance of EAT-2 recruitment and its downstream effectors are not well characterised. We identified PLCγ1 and PLCγ2 as principal binding partners for the EAT-2 tail. Both PLCγ1 and PLCγ2 are functionally important for cytotoxicity in NK92 cells through CD244 (SLAMF4), NTB-A (SLAMF6) and CRACC. Comparison of the specificity of SH2 domains from activating and inhibitory signalling mediators revealed a hierarchy of affinities for CD244 (SLAMF4) ITSMs. While binding of phosphatase SH2 domains to individual ITSMs of CD244 was weak compared with SAP or EAT-2, binding of tandem SH2 domains of SHP-2 to longer peptides containing tandem phosphorylated ITSMs in human CD244 increased the affinity ten fold. The concentration of the tyrosine phosphatase, SHP-2 was in the order of a magnitude higher than the adaptors, SAP and EAT-2. These data demonstrate a mechanism for direct recruitment of phosphatases in inhibitory signalling by ITSMs, while explaining competitive dominance of SAP and EAT-2.

NK cells, innate immunity and hepatitis C infection after liver transplantation

Liver transplantation in patients with active hepatitis C virus (HCV) infection is followed by almost universal recurrence of viral infection. The control of HCV infection has been characterized largely in terms of the HCV-specific function of T-lymphocytes and the adaptive immune response. Emerging data suggest that components of the innate immune system, including natural killer cells, have a central role in determining the nature of posttransplant HCV infection and the likelihood of response to antiviral therapy. This review examines the emerging evidence implicating innate immunity in the pathogenesis of posttransplant HCV infections and the potential therapeutic implications of these observations.

The role of SAP and SLAM family molecules in the humoral immune response

Effective B cell-mediated immunity, including the formation of germinal centers and the generation of high-affinity memory B cells and long-lived plasma cells, is dependent on CD4(+) T cells. Immunodeficiencies that present with defects in the antibody response have provided insights into the molecular mechanisms of B cell responses and the provision of T cell help. One such immunodeficiency is X-linked lymphoproliferative disease (XLP), which results from mutations in SH2D1A, the gene encoding SLAM-associated protein (SAP). Patients with XLP present with humoral defects characterized by hypogammaglobulinemia. We now know that SAP, through its signaling downstream of multiple members of the signaling lymphocytic activation molecule (SLAM) family of cell surface receptors, plays a crucial role in many aspects of this immune response. Here, we discuss the role of SAP in the generation of humoral immunity, particularly T cell-dependent antibody responses and the generation of germinal centers.

Impaired Epstein-Barr virus–specific CD8+ T-cell function in X-linked lymphoproliferative disease is restricted to SLAM family–positive B-cell targets

X-linked lymphoproliferative disease (XLP) is a condition associated with mutations in the signaling lymphocytic activation molecule (SLAM)–associated protein (SAP; SH2D1A). SAP functions as an adaptor, binding to and recruiting signaling molecules to SLAM family receptors expressed on T and natural killer cells. XLP is associated with extreme sensitivity to primary Epstein-Barr virus (EBV) infection, often leading to a lethal infectious mononucleosis. To investigate EBV-specific immunity in XLP patients, we studied 5 individuals who had survived EBV infection and found CD8+ T-cell responses numerically comparable with healthy donors. However, further investigation of in vitro–derived CD8+ T-cell clones established from 2 of these donors showed they efficiently recognized SLAM ligand–negative target cells expressing EBV antigens, but showed impaired recognition of EBV-transformed, SLAM ligand–positive, lymphoblastoid cell lines (LCLs). Importantly, LCL recognition was restored when interactions between the SLAM receptors CD244 and natural killer–, T-, and B-cell antigen (NTBA) and their ligands on LCLs were blocked. We propose that XLP patients' particular sensitivity to EBV, and not to other viruses, reflects at least in part EBV's strict tropism for B lymphocytes and the often inability of the CD8+ T-cell response to contain the primary infection of SLAM ligand–expressing target cells.

The SLAM and SAP gene families control innate and adaptive immune responses

The nine SLAM-family genes, SLAMF1-9, a subfamily of the immunoglobulin superfamily, encode differentially expressed cell-surface receptors of hematopoietic cells. Engagement with their ligands, which are predominantly homotypic, leads to distinct signal transduction events, for instance those that occur in the T or NK cell immune synapse. Upon phosphorylation of one or more copies of a unique tyrosine-based signaling motif in their cytoplasmic tails, six of the SLAM receptors recruit the highly specific single SH2-domain adapters SLAM-associated protein (SAP), EAT-2A, and/or EAT-2B. These adapters in turn bind to the tyrosine kinase Fyn and/or other protein tyrosine kinases connecting the receptors to signal transduction networks. Individuals deficient in the SAP gene, SH2D1A, develop an immunodeficiency syndrome: X-linked lympho-proliferative disease. In addition to operating in the immune synapse, SLAM receptors initiate or partake in multiple effector functions of hematopoietic cells, for example, neutrophil and macrophage killing and platelet aggregation. Here we discuss the current understanding of the structure and function of these recently discovered receptors and adapter molecules in the regulation of adaptive and innate immune responses.

Regulation of cellular and humoral immune responses by the SLAM and SAP families of molecules

SAP (SLAM-associated protein) was identified in 1998 as an adaptor molecule involved in the intracellular signaling pathways elicited through the cell surface receptor SLAM and as the protein defective in the human immunodeficiency X-linked lymphoproliferative disease (XLP). During the past eight years, it has been established that the SLAM family of cell surface receptors (SLAM, 2B4, NTB-A, Ly9, CD84) and the SAP family of adaptors (SAP, EAT-2, ERT) play critical roles in lymphocyte development, differentiation, and acquisition of effector functions. Studies of these proteins have shown unexpected roles in cytokine production by T cells and myeloid cells, T cell-dependent humoral immune responses, NK cell-mediated cytotoxicity, and NKT cell development. This review highlights recent findings that have improved our understanding of the roles of the SLAM and SAP families of molecules in immune regulation and discusses how perturbations in the signaling pathways involving these proteins can result in different disease states.

Signaling Lymphocyte Activation Molecule-Associated Protein Is a Negative Regulator of the CD8 T Cell Response in Mice

The primary manifestation of X-linked lymphoproliferative syndrome, caused by a dysfunctional adapter protein, signaling lymphocyte activation molecule-associated protein (SAP), is an excessive T cell response upon EBV infection. Using the SAP-/- mouse as a model system for the human disease, we compared the response of CD8+ T cells from wild-type (wt) and mutant mice to various stimuli. First, we observed that CD8+ T cells from SAP-/- mice proliferate more vigorously than those from wt mice upon CD3/CD28 cross-linking in vitro. Second, we analyzed the consequence of SAP deficiency on CTL effector function and homeostasis. For this purpose, SAP-/- and wt mice were infected with the murine gamma-herpesvirus 68 (MHV-68). At 2 wk postinfection, the level of viral-specific CTL was much higher in mutant than in wt mice, measured both ex vivo and in vivo. In addition, we established that throughout 45 days of MHV-68 infection the frequency of virus-specific CD8+ T cells producing IFN-gamma was significantly higher in SAP-/- mice. Consequently, the level of latent infection by MHV-68 was considerably lower in SAP-/- mice, which indicates that SAP-/- CTL control this infection more efficiently than wt CTL. Finally, we found that the Vbeta4-specific CD8+ T cell expansion triggered by MHV-68 infection is also enhanced and prolonged in SAP-/- mice. Taken together, our data indicate that SAP functions as a negative regulator of CD8+ T cell activation.

Wild-type p53 activates SAP expression in lymphoid cells

SAP is an adaptor molecule with one SH2 domain and it is expressed in activated T and NK cells, where it is required for the appropriate signaling from the SLAM family of surface receptors. Deleted or mutated SAP genes that encode functionally defective protein are associated with the X-linked lymphoproliferative disease (XLP). This primary immunodeficiency is characterized by extreme sensitivity to Epstein-Barr virus (EBV) infection, dysgammaglobulinemia and a high rate of lymphoma development. The vigorous T- and B-cell proliferation that follows EBV infection and the high incidence of lymphomas (30%) in XLP patients might reflect functional defects in cell cycle and/ or apoptosis control. Our experiments show that SAP is a target of p53. In Burkitt lymphoma (BL) lines transfected with a temperatur-sensitive (ts) p53, SAP mRNA and protein expression was dependent on wild-type (wt) p53. Activation of endogenous wt p53 in BLs and lymphoblastoid cell lines led to the induction of SAP and this was inhibited by the specific p53 inhibitor pifithrin-alpha. Cell lines that carried mutant p53 did not express SAP under similar conditions. Moreover, we have shown binding of wt p53 to the promoter region of SAP by ChIP assay. Our results suggest that SAP contributes to the execution of some p53 functions.

The SAP family of adaptors in immune regulation

SAP and EAT-2 define a new class of adaptor proteins composed almost exclusively of a Src homology 2 (SH2) domain. By way of their SH2 domain, SAP-like adaptors interact with tyrosine-based motifs in the cytoplasmic region of SLAM-related receptors, a family of immune cell-specific molecules involved in immunoregulation. Recent findings indicate that SAP is required for the functions of SLAM family receptors, as a consequence of its ability to promote recruitment of Src-related protein tyrosine kinase FynT and allow SLAM-related receptors to transduce tyrosine phosphorylation signals. SAP is mutated in X-linked lymphoproliferative (XLP) syndrome, a rare inherited human disease characterized by an deregulated immune response to Epstein-Barr virus infection. Several lines of evidence indicate that defects in the activities of SLAM-related receptors caused by SAP deficiency account for the immune dysfunctions associated with XLP.

SAP mediates specific cytotoxic T-cell functions in X-linked lymphoproliferative disease

Cytotoxic T cells (CTLs) and natural killer cells play a major role in the immune response to Epstein-Barr virus (EBV) infection. In X-linked lymphoproliferative (XLP) disease, a severe immunodeficiency, immunodysregulatory phenomena are observed following EBV infection, suggesting that defects exist in these effector populations. The gene defective in XLP is SAP (signaling lymphocytic activation molecule [SLAM]–associated protein), an adaptor protein that mediates signals through SLAM and other immunoglobulin superfamily receptors including 2B4. We generated EBV-specific T-cell lines from controls and XLP patients and examined CTL function in response to different stimuli. We show that XLP patients can generate EBV–T-cell lines that are phenotypically similar to those from controls. XLP patient EBV–T-cell lines showed a significant decrease in interferon-gamma (IFN-γ) production in response to 2B4 and autologous EBV-transformed lymphoblastoid cell line (LCL) stimulation but not in response to SLAM. Furthermore, XLP EBV–T-cell lines demonstrated markedly decreased cytotoxic activity against autologous LCLs. By retroviral gene transfer of the SAP gene into XLP EBV–T-cell lines, we show reconstitution of IFN-γ production and of cytotoxic activity confirming SAP-dependent defects. These studies demonstrate that in XLP the lack of SAP affects specific signaling pathways resulting in severe disruption of CTL function.

Molecular and immunological basis of X-linked lymphoproliferative disease

X-linked lymphoproliferative (XLP) disease is a human immune dysfunction characterized primarily by an inappropriate response to Epstein-Barr virus infection. In 1998, it was discovered that XLP is caused by inactivating mutations in the SAP/SH2D1A/DSHP gene. This gene codes for an immune cell-specific polypeptide termed SAP (SLAM-associated protein) that is composed almost exclusively of an Src homology 2 (SH2) domain. By way of its SH2 domain, SAP interacts with tyrosine-based motifs located in the cytoplasmic region of members of the SLAM (signaling lymphocyte activation molecule) family of receptors. Recent findings indicate that SAP is required for the function of SLAM-related receptors, as a consequence of its capacity to promote the recruitment and activation of the Src-related protein tyrosine kinase FynT, thereby allowing SLAM receptor-mediated protein tyrosine phosphorylation signals in immune cells. Functional and genetic analyses suggest that the phenotype associated with XLP is caused in large part by defects in the functions of SLAM-related receptors due to SAP deficiency.

Human natural killer cell deficiencies and susceptibility to infection

There are a surprisingly large number of human natural killer (NK) cell deficiency states that provide insight into the role of NK cells in defense against human infectious disease. Many disorders associated with NK cell defects are caused by single gene mutations and, thus, give additional understanding concerning the function of specific molecules in NK cell development and activities. A resounding theme of NK cell deficiencies is susceptibility to herpesviruses, suggesting that unexplained severe herpesviral infection should raise the possibility of an NK cell deficit.

SH2D1A expression in Burkitt lymphoma cells is restricted to EBV positive group I lines and is downregulated in parallel with immunoblastic transformation

The SH2 domain containing SH2D1A protein has been characterized in relation to the X-linked lymphoproliferative disease (XLP), a primary immunodeficiency that leads to serious clinical conditions after Epstein-Barr virus (EBV) infection. The SH2D1A gene is mutated in the majority of XLP patients. We previously detected SH2D1A in activated T and NK cells, but not in B lymphocytes. We have found SH2D1A protein in Burkitt lymphoma (BL) lines, but only in those that carried EBV and had a Group I (germinal center) phenotype. All the EBV-carrying Group III (immunoblastic) and the EBV-negative BL lines tested were SH2D1A-negative. Motivated by these differences, we studied the impact of EBV and the cellular phenotype on SH2D1A expression. We approached the former question with BL sublines after both the loss of the virus and subsequent reinfection. We also tested original EBV-negative BL lines carrying transfected EBV genes, such as EBNA1, EBNA2, EBNA6, EBER1, 2 and LMP1, respectively. In our experiments, no direct relationship could be seen between EBV and SH2D1A expression. We modified the phenotype of the Group I BL cells by LMP1 transfection or CD40 ligation. The phenotypic changes, indicated by expression of immunoblastic markers, e.g., SLAM, were accompanied by downregulation of SH2D1A. It seems, therefore, that the presence of EBV and the phenotype of the cell together regulate SH2D1A expression in the BL cells. It is possible that SH2D1A is expressed in a narrow window of B cell development represented by germinal center cells.

From Burkitt's lymphoma to chronic active Epstein-Barr virus (EBV) infection: an expanding spectrum of EBV-associated diseases

Epstein-Barr virus (FBV) is one of 8 known human herpesviruses. EBV infection usually occurs in early childhood and is subclinical. However, primary infection in adolescence or adulthood causes infectious mononucleosis in approximately half of infected individuals. Recently, the spectrum of human diseases associated with EBV injection has increased, primarily due to methodological advances in EBV detection. Initially, EBV was isolated from a cultured Burkitt lymphoma cell line, and has been felt to be etiologically linked to the development of Burkitt lymphoma, as well as other human malignancies. This review mainly focuses on pathogenetic mechanisms, many of which remain enigmatic, for the various human diseases, which are considered to be associated with EBV injection.

Distinct interactions of the X-linked lymphoproliferative syndrome gene product SAP with cytoplasmic domains of members of the CD2 receptor family

X-linked lymphoproliferative syndrome (XLP; Duncan's disease) is a primary immunodeficiency disease that manifests as an inability to regulate the immune response to Epstein-Barr virus (EBV) infection. Here we examine the ability of the product of the gene defective in XLP, SAP (DSHP/SH2D1A), to associate with the cytoplasmic domains of several members of the CD2 subfamily of cell surface receptors, including SLAM, 2B4, and CD84. While recruitment of SAP to SLAM occurred in a phosphorylation-independent manner, SAP was found to bind preferentially to tyrosine-phosphorylated cytoplasmic domains within 2B4 and CD84. Missense or nonsense mutations in the SAP open reading frame were identified in five of seven clinically diagnosed XLP patients from different kindreds. Four of these variants retained the ability to bind to the cytoplasmic tails of SLAM and CD84. While ectopic expression of wild-type SAP was observed to block the binding of SHP-2 to SLAM, mutant SAP derivatives that retained the ability to bind SLAM did not inhibit recruitment of SHP-2 to SLAM. In contrast, SAP binding to CD84 had no effect on the ability of CD84 to recruit SHP-2, but instead displaced SHP-1 from the cytoplasmic tail of CD84. These results suggest that mutations in the gene encoding the XLP protein SAP lead to functional defects in the protein that include receptor binding and SHP-1 and SHP-2 displacement and that SAP utilizes different mechanisms to regulate signaling through the CD2 family of receptors.

Lymphocytic vasculitis in X-linked lymphoproliferative disease

Systemic vasculitis is an uncommon manifestation of X-linked lymphoproliferative disease (XLP), a disorder in which there is a selective immune deficiency to Epstein-Barr virus (EBV). The molecular basis for XLP has recently been ascribed to mutations within SLAM-associated protein (SAP), an SH2 domain-containing protein expressed primarily in T cells. The authors describe a patient who died as a result of chronic systemic vasculitis and fulfilled clinical criteria for the diagnosis of XLP. Sequencing of this patient's SAP gene uncovered a novel point mutation affecting the SH2 domain. The patient presented with virus-associated hemophagocytic syndrome (VAHS) and later had chorioretinitis, bronchiectasis, and hypogammaglobulinemia develop. He further developed mononeuritis and fatal respiratory failure. Evidence of widespread small and medium vessel vasculitis was noted at autopsy with involvement of retinal, cerebral, and coronary arteries as well as the segmental vessels of the kidneys, testes, and pancreas. Immunohistochemical analysis using antibodies to CD20, CD45RO, and CD8 revealed that the vessel wall infiltrates consisted primarily of CD8(+) T cells, implying a cytotoxic T-lymphocyte response to antigen. EBV DNA was detected by polymerase chain reaction (PCR) in arterial wall tissue microdissected from infiltrated vessels further suggesting that the CD8(+) T cells were targeting EBV antigens within the endothelium. The authors propose that functional inactivation of the SAP protein can impair the immunologic response to EBV, resulting in systemic vasculitis.

Patients with X-linked lymphoproliferative disease have a defect in 2B4 receptor-mediated NK cell cytotoxicity

Patients with the X-linked lymphoproliferative disorder (XLPD) are unable to control Epstein-Barr virus (EBV)-induced infections and lymphoproliferation. This disease is caused by a deficit of SAP, an adapter protein involved in the signal transduction of several cell surface receptors of the CD2 superfamily. One of these receptors, called 2B4, is expressed on NK cells, cytotoxic T cells and myeloid cells and activates NK cell cytotoxicity. Here we show that XLPD patients have a defect of 2B4 receptor-mediated NK cell cytotoxicity. This defect may contribute to the pathogenesis of XLPD by reducing NK cell lysis of EBV-infected B cells.

Defective NK cell activation in X-linked lymphoproliferative disease

X-linked lymphoproliferative disease (XLP) is characterized by a selective immune deficiency to EBV. The molecular basis of XLP has been attributed to mutations of signaling lymphocytic activation molecule-associated protein, an intracellular molecule known to associate with the lymphocyte-activating surface receptors SLAM and 2B4. We have identified a single nucleotide mutation in SLAM-associated protein that affects the NK cell function of males carrying the mutated gene. In contrast to normal controls, both NK and lymphokine-activated killer cell cytotoxicity was significantly reduced in two XLP patients. In addition to decreased baseline cytotoxicity, ligation of 2B4 significantly augmented NK lytic function in normal controls but failed to enhance the cytotoxicity of NK cells from XLP patients. These findings suggest that association of SAP with 2B4 is necessary for optimal NK/lymphokine-activated killer cytotoxicity and imply that alterations in SAP/2B4 signaling contribute to the immune dysfunction observed in XLP.

The abnormal gene in X-linked lymphoproliferative syndrome

The gene defect responsible for X-linked lymphoproliferative syndrome, SH2D1A (SH2-domain-containing gene 1A), was recently cloned. This gene encodes a small protein of 128 amino acids containing a single SH2 domain, which is thought to play an important role in signal transduction in activated T cells. The definition of SH2D1A protein function will provide insight into the pathogenesis of fatal Epstein-Barr virus infection, lymphomas, Hodgkins disease, immunodeficiency, aplastic anemia and lymphohistiocytic disorders that characterize the syndrome.

Epstein-Barr virus-infected B cells of males with the X-linked lymphoproliferative syndrome stimulate and are susceptible to T-cell-mediated lysis

Primary infection with the Epstein-Barr virus (EBV) results in fatal infectious mononucleosis in up to 70% of males affected by the X-linked lymphoproliferative syndrome (XLP). This rare disease is often associated with diverse natural killer (NK)-, B- and T-cell deficiencies. We describe experiments testing whether the B lymphocytes of affected males play a role in the pathogenesis of XLP due to a low susceptibility to T-cell-mediated immunity. Using reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry we detected in these B cells the expression of viral proteins EBNA-1, EBNA-2, EBNA-3A, EBNA-3C, LMP-1 and LMP-2A, which provide targets for cytotoxic T cells. Major histocompatibility complex (MHC) class I, MHC class II and the B7 costimulatory molecule were present on the cell surface. Accordingly, the EBV-infected B cells were lysed in 51Cr-release assays by T lymphocytes sharing MHC determinants with the targets. This MHC-restricted and specific lysis was confirmed in competition experiments using MHC-specific monoclonal antibodies (MAbs) and synthetic peptides. XLP-derived LCLs could also induce MHC class I-restricted memory and cytotoxic T lymphocytes. Thus, these XLP-derived B cells resembled normal LCIs in vitro with respect to induction of EBV-specific cytotoxic T cells (CTL), the ability to present EB viral antigens and the susceptibility to EBV-specific and MHC-restricted CTL-mediated killing. The failure of the immune system to eliminate these virus-infected B cells in XLP is clearly not caused by a B-cell-specific defect.

Simple assay for evaluation of Epstein-Barr virus specific cytotoxic T lymphocytes

Epstein-Barr virus (EBV)-specific cytotoxic T lymphocytes (CTL) are considered to be one of major defenses against the activation of EBV infection. We have developed a simple assay for evaluation of EBV-CTL by means of culturing peripheral blood mononuclear cells at the concentration of 2 x 10(6) cells/ml infected by B95-8 EBV, in the presence or absence of cyclosporin A (CSA). No lymphoblastoid cell line was established from ten EBV-seropositive healthy individuals in the absence of CSA. In contrast, cell lines were established from ten EBV-seronegative healthy individuals in the absence of CSA, indicating lack of EBV-CTL in these individuals. Methods described herein are simple and correlate well with EBV-CTL activity when compared to conventional methods, such as outgrowth regression or chromium-51 release assays.

Defective activity of Epstein-Barr virus (EBV) specific cytotoxic T lymphocytes in children with chronic active EBV infection and in their parents

Antibodies of Epstein-Barr virus (EBV), EBV-specific cytotoxic T lymphocyte (EBVCTL) activity and the lymphocyte subset of CTL were examined in 13 Japanese children with chronic active EBV infection (CAEBV) and their parents (eight fathers and 10 mothers). Anti-virus-capsid antigen (VCA)-IgG antibody titers ranged from 1:640 to 1:5120 in the patients with CAEBV and from 1:40 to 1:640 in the parents. While anti-VCA-IgM antibody was detected in three patients, anti-VCA-IgA antibody in five and anti-early-antigen (EA)-IgG antibody in 11, no antibody was detected in the parents except anti-EA antibody, which was positive in the mothers of cases 5 and 13 (1:10 and 1:40). Anti-EBV-associated nuclear antigen (EBNA) antibody was < or = 1:10 in six out of 13 patients with CAEBV and in 10 out of 18 parents tested. Epstein-Barr virus activity was significantly lower (P < 0.005) both in the children with CAEBV and in their parents than in seropositive age-matched controls. Proportions of a CTL subset (CD8+ CD11- lymphocytes) in the patients with CAEBV were significantly higher (P < 0.005) than in controls, while those in the parents were at the same level as in controls. Defective EBVCTL activity and anti-EBNA-antibody responses were frequently observed both in children with CAEBV and in their parents, which may suggest that the abnormal immune response to EBV may be based on a familial disorder, though no familial involvement has been reported in Japanese children with CAEBV.

The X-linked lymphoproliferative disease: from autopsy toward cloning the gene 1975-1990

Although X-linked lymphoproliferative disease (XLP) is rare (1-2 males per 1 x 10(6)), it serves as a model for discerning diverse diseases caused by Epstein-Barr virus (EBV) ranging from agammaglobulinemia to fatal infectious mononucleosis following infection with the virus. The study of patients with XLP has also paved the way to understanding how EBV induce diseases in children with primary immunodeficiency diseases, organ transplant recipients, and those with acquired immunodeficiency syndrome. This review is dedicated to the memory of Gordon Vawter, M.D., who generously provided insights into the causes of pathogenesis of immune deficiency and lymphoproliferative disorders.

Defective control of Epstein-Barr virus-infected B cell growth in patients with X-linked lymphoproliferative disease

We studied the cellular function and lymphokine production of T cells from patients with X-linked lymphoproliferative disease (XLP) when activated by the challenge with Epstein-Barr virus (EBV) infection. We used an assay system in which T cells were stimulated with membrane antigens of autologous EBV-infected B lymphoblastoid cell lines (B-LCL) and we examined cellular and humoral factors derived from the stimulated T cells which control the growth of EBV-infected B-LCL. Immunoglobulin secretion from the autologous B-LCL was suppressed with radiosensitive suppressor cells in the patients with XLP. The degree of suppression was correlated with the immunoglobulin levels in the serum of the patients with acquired hypogammaglobulinaemia (P less than 0.05). In addition, T cells from the patients with XLP failed to produce interferon-gamma (IFN-gamma) (P less than 0.001). Moreover, the T cell supernatants from the patients with XLP were less potent to inhibit the B-LCL growth. This diminished inhibition of the B-LCL growth was correlated well with the decreased concentration of IFN-gamma in the T cell supernatants. These findings suggest that suppressor cells may be activated in the patients with the hypogammaglobulinaemia phenotype of XLP, but the frequent development of B cell lymphoma in hypogammaglobulinaemia indicate that immunoglobulin suppression may not exert enough pressure on the in vivo growth of EBV-infected B cells. The defective secretion of IFN-gamma may be, at least partially, responsible for the abnormal cytotoxic T cell and natural killer activities found in the patients with XLP, and may indicate the clinical evaluation about the preventive injection of IFN-gamma against the development of malignant lymphoma.

Detection of X-linked lymphoproliferative disease using molecular and immunovirologic markers

PURPOSE, PATIENTS, AND METHODS

Detection of males affected with the X-linked lymphoproliferative disease (XLP) was sought using immunovirologic and molecular genetic linkage techniques. The study population consisted of 20 males in six families with XLP.

RESULTS

Concordance for detection of affected males was 100% when linkage analysis using DXS42 and DXS37 DNA probes and antibody responses to challenge with bacteriophage phi X174 were both determined. Most affected males showing IgG subclass immune deficiency could not produce antibodies to Epstein-Barr virus nuclear antigen and had deficient responses to challenge with bacteriophage phi X174.

CONCLUSION

Use of only one of the techniques described can fail to lead to the diagnosis of XLP, because problems can prevail with each individual determination.

Viruses and antibody deficiency syndromes

Viral infections that occur in patients with primary immunodeficiencies are summarized. These viral infections include: Echovirus, poliovirus, varicella zoster, non-A non-B hepatitis and hepatitis B. Cases of X-linked lymphoproliferative syndrome associated with Epstein-Barr virus infection and congenital rubella syndrome are also reviewed. In the second part of the paper, retrovirus (HIV) isolations from blood mononuclear cells of 3 out of 31 patients with common variable hypogammaglobulinemia are reported. This supports the concept that some of the non-familial "primary" immunodeficiencies may be due to retrovirus infections.

Stress-related immune suppression: health implications

This study used a year-long prospective design to assess linkages among distress, immunity, and illness. Serial blood samples were collected from 40 first-year medical students at the first, third, and fifth examination periods, as well as 1 month before each. There were significant decrements in the production of gamma-interferon by concanavalin A-stimulated lymphocytes obtained at the time of examinations. Antibody titers to Epstein-Barr virus (EBV) increased during examination periods, suggesting reactivation of latent EBV and therefore poorer cellular immune control of latent virus. We obtained data that suggest that T-cell killing by memory T lymphocytes of EBV transformed autologous B lymphocytes also declined during examination periods. The activity of a lymphokine, leukocyte migration inhibition factor, normally suppressed during recrudescence of herpes simplex virus type 2 infections, was altered during examination periods and an increase in both plasma and intracellular levels of cyclic AMP associated with examination stress was observed. An increase in the incidence of self-reported symptoms of infectious illness was also associated with examination periods. The data support the linkage between stress-related immunosuppression and health.

Stress, loneliness, and changes in herpesvirus latency

This study used a prospective design to examine the influence of examination stress and loneliness on herpesvirus latency as measured by changes in antibody levels to three herpesviruses, Epstein-Barr virus (EBV), Herpes simplex type I (HSV-1), and cytomegalovirus (CMV). Three blood samples were obtained from 49 first-year medical students, with the first sample drawn 1 month before final examinations, the second on the first day of final examinations, and the third during the first week after their return from summer vacation. A median split on the UCLA Loneliness Scale divided subjects into high- and low-scoring loneliness groups. There were significant changes in the antibody titers to all three herpesviruses across the sample points, with the lowest levels found in the third (low stress) sample. High-loneliness subjects had significantly higher EBV antibody titers than low-loneliness subjects. These data suggest that stress-related immunosuppression can significantly modulate herpesvirus latency.

Role of Epstein-Barr virus in acquired immune deficiency syndrome

We have reviewed the biologic characteristics, immune responses, and diverse array of diseases occurring from Epstein-Barr virus infections in immune deficient patients. We have summarized possible roles of the virus in the risk groups for AIDS. Data is convincing that EBV is responsible for some of the cases of lymphadenomegaly and Burkitt-like, non-Hodgkin's lymphomas in patients with pre-AIDS and AIDS. A hypothesis has been proposed wherein EBV and other stimulants of B and T cells allow productive infection by the retrovirus and spread of HTLV-III throughout the helper T cell populations.

Epstein-Barr virus specific T-cell response in nasopharyngeal carcinoma patients

There is a substantial body of evidence suggesting an association between Epstein-Barr virus (EBV) and undifferentiated nasopharyngeal carcinoma (NPC). The present study has compared a group of NPC patients (newly diagnosed and long-term survivors) and controls for EBV-specific T-cell immunity using the regression of transformation assay. Newly diagnosed patients (17 tested) when compared with either long-term survivors (20 tested) or controls (30 tested) showed a significant impairment in virus-specific T-cell immunity (p = 0.036, p = 0.043 respectively). Furthermore, donors with IgA antibody to EBV showed a significant depression in virus-specific T-cell immunity compared with donors without IgA antibody (19 IgA-positive, 48 IgA-negative; p = 0.0025). These results may be important in explaining the postulated role of EBV in the aetiology of NPC.

Oncological consequences of impaired immune surveillance against ubiquitous viruses

The immune system is constantly challenged by ubiquitous viruses. Multiple immune defenses have evolved to meet these challenges, and thus immunocompetent individuals successfully respond to infection without sequela. X-linked lymphoproliferative syndrome patients, renal allograft recipients, and acquired immunodeficiency syndrome patients share impaired immune surveillance as a common feature. Such individuals are variously susceptible to numerous untoward complications following infection with Epstein-Barr virus, cytomegalovirus, herpes simplex virus, human papillomavirus, and hepatitis B virus. We hypothesize that failure of the immune system to control these viruses is instrumental in the occurrence of some B-cell lymphomas. Kaposi's sarcoma, and squamous-cell and hepatocellular carcinomas. Herein we review some mechanisms responsible for the breakdown of immune surveillance and the permissive role immunodeficiency plays in viral oncogenesis.