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

Molecular and cellular pathogenesis of X-linked lymphoproliferative disease

X-linked lymphoproliferative disease (XLP) is an inherited immune defect caused by mutations in the Src homology 2 domain-containing gene 1A, which encodes the adapter protein, signaling lymphocytic activation molecule (SLAM)-associated protein (SAP). SAP is expressed in T cells, natural killer (NK) cells, and NKT cells, where it binds to the cytoplasmic domain of the surface receptor SLAM (CD150) and the related receptors, 2B4 (CD244), CD84, Ly9 (CD229), NK-T-B-antigen, and CD2-like receptor-activating cytotoxic T cells. SAP also binds to the Src family tyrosine kinase Fyn and recruits it to SLAM, which leads to the generation of downstream phosphotyrosine signals. While the roles of the SLAM family receptors are only beginning to be understood, experiments suggest that these molecules regulate important aspects of lymphocyte function, such as proliferation, cytokine secretion, cytotoxicity, and antibody production. Thus, in XLP patients who lack functional SAP, the SLAM family receptors may not signal properly. This property likely contributes to the phenotypes of XLP, including fulminant infectious mononucleosis, lymphoma, and hypogammaglobulinemia. Further studies of SAP and the SLAM family receptors will provide insights into XLP and elucidate the signaling events regulating lymphocyte ontogeny and function.

Defective B cell responses in the absence of SH2D1A

More than half of patients with X-linked lympho-proliferative disease, which is caused by a defect in the intracellular adapter protein SH2D1A, suffer from an extreme susceptibility to Epstein-Barr virus. One-third of these patients, however, develop dysgammaglobulenemia without an episode of severe mononucleosis. Here we show that in SH2D1A(-/-) mice, both primary and secondary responses of all Ig subclasses are severely impaired in response to specific antigens. Because germinal centers were absent in SH2D1A(-/-) mice upon primary immunization, and because SH2D1A was detectable in wt germinal center B cells, we examined whether SH2D1A(-/-) B cell functions were impaired. Using the adoptive cotransfer of B lymphocytes from hapten-primed SH2D1A(-/-) mice with CD4(+) T cells from primed wt mice into irradiated wt mice provided evidence that signal transduction events controlled by SH2D1A are essential for B cell activities resulting in antigen specific IgG production. Defects in naive SH2D1A(-/-) B cells became evident upon cotransfer with non-primed wt CD4(+) cells into Rag2(-/-) recipients. Thus, both defective T and B cells exist in the absence of SH2D1A, which may explain the progressive dysgammaglobulinemia in a subset of X-linked lympho-proliferative disease patients without involvement of Epstein-Barr virus.

The SAP and SLAM families in immune responses and X-linked lymphoproliferative disease

SAP (signalling lymphocytic activation molecule (SLAM)-associated protein) is a T- and natural killer (NK)-cell-specific protein containing a single SH2 domain encoded by a gene that is defective or absent in patients with X-linked lymphoproliferative syndrome (XLP). The SH2 domain of SAP binds with high affinity to the cytoplasmic tail of the haematopoietic cell-surface glycoprotein SLAM and five related receptors. SAP regulates signal transduction of the SLAM-family receptors by recruiting SRC kinases. Similarly, the SAP-related proteins EAT2A and EAT2B are thought to control signal transduction that is initiated by SLAM-related receptors in professional antigen-presenting cells. In this review, we discuss recent findings on the structure and function of proteins of the SAP and SLAM families.

The X-linked lymphoproliferative disease gene product SAP is expressed in activated T and NK cells

The unique manifestation of the inherited immunodeficiency, X-linked lymphoproliferative disease (XLP), is the impaired control of EBV infection. The gene, which carries mutations or is deleted in the patients, has been identified (Xq25). The encoded protein (SAP, 128 aa) contains a single SH2 domain and binds to signaling lymphocytic activation molecule (SLAM) and to other related surface molecules that are expressed on activated T, B and NK cells. SAP modifies signal transduction through its association with these molecules. Initially it was assumed that SAP acts passively by interfering and blocking active interactions involving other SH2 carrying molecules. We demonstrated that SAP protein is expressed in activated T and NK, but not in activated B cells. This finding is in line with the fact that in vitro performance of effector cells derived from XLP patients is impaired. However, it is still not known why the severe symptoms (fatal mononucleosis or malignant lymphoproliferation in the survivors of the primary infection) are elicited by EBV. We studied SAP expression in several Burkitt lymphoma (BL) derived lines. In contrast to normal B cells, certain lines expressed SAP. These were all type I cells in the Burkitt line nomenclature: they expressed only one of the EBV encoded proteins (EBNA-1) and their phenotype corresponded to resting B cells. Lymphoblastoid cell lines and type III BLs, whose phenotype resembled activated B cells and expressed all nine EBV encoded proteins, were devoid of SAP. The relationship between cell activation and SAP expression is reciprocal in T and B cells i.e. BL lines, activated T and NK cells express SAP, while BL blasts do not express SAP. This opposite relationship may be exploited for studies about the function of SAP.

Immune regulation in Epstein-Barr virus-associated diseases

Epstein-Barr virus (EBV) is a member of the human herpesvirus family and, like many other herpesviruses, maintains a lifelong latent association with B lymphocytes and a permissive association with stratified epithelium in the oropharynx. Clinical manifestations of primary EBV infection range from acute infectious mononucleosis to an asymptomatic persistent infection. EBV is also associated with a number of malignancies in humans. This review discusses features of the biology of the virus, both in cell culture systems and in the natural host, before turning to the role of the immune system in controlling EBV infection in healthy individuals and in individuals with EBV-associated diseases. Cytotoxic T cells that recognize virally determined epitopes on infected cells make up the major effector arm and control the persistent infection. In contrast, the options for immune control of EBV-associated malignancies are more restricted. Not only is antigen expression restricted to a single nuclear antigen, EBNA1, but also these tumor cells are unable to process EBV latent antigens, presumably because of a transcriptional defect in antigen-processing genes (such as TAP1 and TAP2). The likelihood of producing a vaccine capable of controlling the acute viral infection and EBV-associated malignancies is also discussed.

Fatal infectious mononucleosis: a severe complication in the treatment of Crohn's disease with azathioprine

A 19 year old man with a history of Crohn's disease treated with azathioprine and prednisone, died after a primary infection with Epstein-Barr virus. He had the characteristics of the virus associated haemophagocytic syndrome, a rare complication of viral infections, which consists of fever, constitutional symptoms, hepatosplenomegaly, liver function and coagulation abnormalities, and hypertriglyceridaemia. Additionally, there was pain, cytopenia, and histiocytic hyperplasia in the bone marrow, spleen, or lymph nodes. This severe complication has been reported previously in renal transplant patients, but not in those with inflammatory bowel disease taking azathioprine. The immunosuppressive therapy may have contributed to this fatal complication of infectious mononucleosis, and this complication should be considered when treating a patient with inflammatory bowel disease with azathioprine.

Evaluation of families wherein a single male manifests a phenotype of X-linked lymphoproliferative disease (XLP)

The Epstein-Barr virus (EBV)-induced diseases of males with X-linked lymphoproliferative disease (XLP) include fatal infectious mononucleosis (IM), non-Hodgkin lymphoma (ML), agammaglobulinemia, and aplastic anemia. These phenotypes also occur as sporadic cases in families, and EBV seronegative males in these families must be considered at risk for XLP until they seroconvert normally to EBV. Given that 50% of males inheriting the defective XLP gene die following primary EBV infection, it is vital that they be identified pre-EBV infection. Here we report results using molecular genetic techniques to provide information as to the relative risks of EBV negative males and potential carrier females in ten families wherein a single male had died of IM.

First prenatal diagnosis of X-linked lymphoproliferative disease

A family study was performed in order to diagnose X-linked lymphoproliferative (XLP) disease in a fetus. The molecular genetic analysis indicated that the fetus, as well as its healthy 7-year-old brother, inherited XLP. Analysis of immunoglobulin subclasses from the 7-year-old brother supported the DNA-based diagnosis. This is the first XLP family of African descent.

Report on the X-linked lymphoproliferative disease in an Australian family

X-linked lymphoproliferative disease is characterized by immune deficiency, particularly to the Epstein-Barr virus and by a tendency to develop fatal infectious mononucleosis, acquired hypogammaglobulinaemia or malignant lymphoma. This disorder has been diagnosed in three boys, two brothers and a maternally related cousin, residing in Australia. The proband presented at 6 years of age with fulminating infectious mononucleosis. His 9 year old male cousin had developed an ileal Burkitt lymphoma one year earlier. Immunological and molecular genetic evidence is presented to support our view that his younger sibling is also affected with this condition. DNA linkage studies using probes to DXS10 and DXS37 provide confirmatory evidence for the diagnosis in the proband's brother and information on carrier status in female family members.

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.

SCID mouse model of Epstein-Barr virus-induced lymphomagenesis of immunodeficient humans

Immunodeficient humans are at very high risk of developing Epstein-Barr virus (EBV)-induced lymphomagenesis. Severe combined immunodeficient mice (SCID) have been shown to develop lymphoproliferative disease (LPD) following transfer of peripheral blood leukocytes (PBL) with latent EBV. To study mechanisms of lymphomagenesis, we compared results of engraftment of PBL from normal donors and immunodeficient donors with X-linked lymphoproliferative disease (XLP). Graft-versus-host disease (GVHD) developed in 6 of 10 SCID mice 4 to 8 weeks following transfer of PBL from normal donors. In contrast, none of 9 mice engrafted with PBL from XLP patients with T-cell defects showed GVHD. LPD developed in mice regardless of the immune competence of the donors. The expression of EBV-encoded proteins, results of immunophenotyping, and karyotyping of the LPD lesions revealed lethal oligoclonal LPD owing to transfer of latent EBV in B cells in mice engrafted with PBL from seropositive donors. Polyclonal LDP developed in mice engrafted with PBL from seronegative patients which were infected with B95-8 virus 6 weeks after transfer of the cells. This model is useful for investigating mechanisms of EBV-induced LDP in immunodeficient patients.

Methods of detection of new families with X-linked lymphoproliferative disease

During the past decade, 240 males with X-linked lymphoproliferative disease (XLP) within 59 unrelated kindreds have been identified worldwide. One half of the patients have developed fatal infections mononucleosis, about one third have acquired hypogammaglobulinemia, and another one fourth have developed malignant lymphoma. Less commonly occurring phenotypes include hyperimmunoglobulinemia M, bone marrow hypoplasia, and necrotizing lymphoid vasculitis. The fatal infectious mononucleosis phenotype occurs at about 2.5 years of age, and median survival is only 33 days following onset of illness. The acquired hypogammaglobulinemia and malignant lymphoma phenotypes are associated with longer survivals, but to date no patient has been documented as living into the fifth decade of life. We summarized recent research findings and technological advances that permit accurate diagnosis of carrier females and detection of males with the XLP gene before Epstein-Barr virus infection.

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.

Expression of Epstein-Barr virus-encoded proteins and B-cell markers in fatal infectious mononucleosis

We assessed 33 lymphoid tissues from 15 patients, including 7 with X-linked lymphoproliferative disease (XLP) and 8 patients with sporadic fatal infectious mononucleosis (IM), to determine whether the cellular infiltrate had the immunophenotype and expressed Epstein-Barr virus (EBV)-encoded proteins characteristic of either EBV-immortalized lymphoblastoid cell lines (LCL) or EBV-carrying Burkitt lymphoma (BL) cells. The results of these studies revealed that in 13 cases the proliferating B cells were polyclonal, LCL-like, and in 2 cases they were monoclonal, malignant lymphoma-like.