Leonard L. Dragone

Src-like adaptor protein regulates TCR expression on thymocytes by linking the ubiquitin ligase c-Cbl to the TCR complex.

The adaptor molecule SLAP and E3 ubiquitin ligase c-Cbl each regulate expression of T cell receptor (TCR)–CD3 on thymocytes. Here we provide genetic and biochemical evidence that both molecules function in the same pathway. TCR-CD3 expression was similar in the absence of SLAP and/or c-Cbl. SLAP and c-Cbl were found to interact, and their expression together downregulated CD3ε. This required multiple domains in SLAP and the ring finger of c-Cbl. Furthermore, expression of SLAP and c-Cbl together induced TCRζ ubiquitination and degradation, preventing the accumulation of fully assembled recycling TCR complexes. These studies indicate that SLAP links the E3 ligase activity of c-Cbl to the TCR, allowing for stage-specific regulation of TCR expression.

Src-like adaptor protein down-regulates T cell receptor (TCR)–CD3 expression by targeting TCRζ for degradation

Src-like adaptor protein (SLAP) down-regulates expression of the T cell receptor (TCR)–CD3 complex during a specific stage of thymocyte development when the TCR repertoire is selected. Consequently, SLAP−/− thymocytes display alterations in thymocyte development. Here, we have studied the mechanism of SLAP function. We demonstrate that SLAP-deficient thymocytes have increased TCRζ chain expression as a result of a defect in TCRζ degradation. Failure to degrade TCRζ leads to an increased pool of fully assembled TCR–CD3 complexes that are capable of recycling back to the cell surface. We also provide evidence that SLAP functions in a pathway that requires the phosphorylated TCRζ chain and the Src family kinase Lck, but not ZAP-70 (ζ-associated protein of 70 kD). These studies reveal a unique mechanism by which SLAP contributes to the regulation of TCR expression during a distinct stage of thymocyte development.

PTPRC ( CD45 ) is not associated with the development of multiple sclerosis in U.S. patients

A C→G nucleotide transition in exon 4 of PTPRC (encoding protein-tyrosine phosphatase receptor-type C, also known as CD45) was recently reported to be genetically associated with the development of multiple sclerosis (MS). We performed an extensive evaluation of this polymorphism using large family-based and case-control comparisons. Overall, we observed no evidence of genetic association between the PTPRC polymorphism and MS susceptibility or disease course.

SLAP, a regulator of immunoreceptor ubiquitination, signaling, and trafficking

Summary:  Src‐like adapter proteins (SLAP and SLAP‐2) constitute a family of proteins that are expressed in a variety of cell types but are studied most extensively in lymphocytes. They have been shown to associate with proximal components of the T‐cell receptor (TCR) and B‐cell receptor (BCR) signaling complexes. An interaction of SLAP with c‐Cbl leads to the ubiquitination and degradation of phosphorylated components of the TCR‐ and BCR‐signaling complexes. The absence of this process in immature SLAP‐deficient T and B cells leads to increased immunoreceptor levels due to decreased intracellular retention and degradation. We propose a model in which SLAP‐dependent regulation of immunoreceptor levels allows for finer control of immunoreceptor signaling. Thus, SLAP functions to dampen immunoreceptor signaling, thereby influencing lymphocyte development and repertoire selection.

Src-Like Adaptor Protein Regulates B Cell Development and Function

The avidity of BCRs and TCRs influences signal strength during processes of lymphocyte development. Avidity is determined by both the intrinsic affinity for Ag and surface levels of the Ag receptor. The Src-like adaptor protein (SLAP) is a regulator of TCR levels on thymocytes, and its deficiency alters thymocyte development. We hypothesized that SLAP, which is expressed in B cells, also is important in regulating BCR levels, signal strength, and B cell development. To test this hypothesis, we analyzed the B cell compartment in SLAP-deficient mice. We found increased splenic B cell numbers and decreased surface IgM levels on mature, splenic B cells deficient in SLAP. Immature bone marrow and splenic B cells from BCR-transgenic, SLAP-deficient mice were found to express higher surface levels of IgM. In contrast, mature splenic B cells from BCR-transgenic mice expressed decreased levels of surface BCR associated with decreased calcium flux and activation-induced markers, compared with controls. These data suggest that SLAP regulates BCR levels and signal strength during lymphocyte development.

Src-like adaptor protein (SLAP) regulates B cell receptor levels in a c-Cbl-dependent manner

Src-like adaptor protein (SLAP) and c-Cbl recently have been shown to cooperate in regulating T cell receptor (TCR) levels in developing T cells. SLAP also is expressed in developing B cells, and its deficiency leads to alterations in B cell receptor (BCR) levels and B cell development. Hence, we hypothesized that SLAP and c-Cbl may cooperate during B cell development to regulate BCR levels. In mice deficient in both SLAP and c-Cbl, we found that B cell development is altered, suggesting that they function through intersecting pathways. To study the mechanism by which SLAP and c-Cbl alter BCR levels, we coexpressed them in a mature mouse B cell line (Bal-17). First we determined that SLAP associates with proximal components of the BCR complex after stimulation and internalization. Coexpression of SLAP and c-Cbl in Bal-17 led to decreased surface and total BCR levels. This decrease in BCR levels depended on intact Src homology 2 (SH2) and C-terminal domains of SLAP. In addition, a mutation in the SH2 domain of SLAP blocked its colocalization with c-Cbl and the BCR complex, whereas deletion of the C terminus did not affect its localization. Last, coexpression of SLAP and c-Cbl altered BCR complex recycling. This alteration in BCR complex recycling depended on enzymatically active c-Cbl and Src family kinases, as well as the intact SH2 and C-terminal domains of SLAP. These data suggest that SLAP has a conserved function in B and T cells by adapting c-Cbl to the antigen-receptor complex and targeting it for degradation.

The ubiquitin ligase Cbl-b limits Pseudomonas aeruginosa exotoxin T–mediated virulence

Pseudomonas aeruginosa, an important cause of opportunistic infections in humans, delivers bacterial cytotoxins by type III secretion directly into the host cell cytoplasm, resulting in disruption of host cell signaling and host innate immunity. However, little is known about the fate of the toxins themselves following injection into the host cytosol. Here, we show by both in vitro and in vivo studies that the host ubiquitin ligase Cbl-b interacts with the type III-secreted effector exotoxin T (ExoT) and plays a key role in vivo in limiting bacterial dissemination mediated by ExoT. We demonstrate that, following polyubiquitination, ExoT undergoes regulated proteasomal degradation in the host cell cytosol. ExoT interacts with the E3 ubiquitin ligase Cbl-b and Crk, the substrate for the ExoT ADP ribosyltransferase (ADPRT) domain. The efficiency of degradation is dependent upon the activity of the ADPRT domain. In mouse models of acute pneumonia and systemic infection, Cbl-b is specifically required to limit the dissemination of ExoT-producing bacteria whereas c-Cbl plays no detectable role. To the best of our knowledge, this represents the first identification of a mammalian gene product that is specifically required for in vivo resistance to disease mediated by a type III-secreted effector.

Vaccine strain varicella-zoster virus-induced central nervous system vasculopathy as the presenting feature of DOCK8 deficiency.

To the Editor: In contrast to autosomal dominant forms of hyper-IgE syndrome resulting from mutations in the STAT3 gene, autosomal recessive dedicator of cytokinesis 8 (DOCK8) deficiency, results in susceptibility to cutaneous viral infections, eosinophilia, and allergic disease. CNS manifestations have been reported in patients with DOCK8 deficiency, but progressive multifocal leukoencephalopathy caused by JC virus has been considered the only known viral etiology to date (1, 2). A 6 year-old boy with atopy and recurrent peripheral blood eosinophilia developed acute intermittent vomiting, diarrhea, headache, and dizziness. Magnetic resonance imaging (MRI) of the brain was normal. One day later, he began giggling inappropriately, experienced left leg paresthesias, urinary incontinence, and fell upon attempting to stand. Repeat MRI with axial diffusion-weighted images revealed multiple areas of acute infarction in areas supplied by both anterior cerebral arteries, a branch of the anterior cerebral artery, the right posterior cerebral artery, and the left middle cerebral artery (Figure 1A). A complete blood count revealed a total eosinophil count of 2,160/μL, but no other abnormalities. He was treated with acetylsalicylic acid and intravenous methylprednisolone followed by oral prednisolone, 2 mg/kg for 3 days after which prednisolone was maintained at 1 mg/kg daily. Figure 1 Manifestation of vaccine strain varicella zoster virus-induced central nervous system vasculopathy On presentation to us one month later, he had developed paresthesias of his hands. Neurological examination showed only mild weakness in the hands. Computed tomography angiogram revealed diffuse vasculopathy. Subsequent 3-dimensional time of flight magnetic resonance angiographic imaging of the circle of Willis revealed vascular narrowing and post-stenotic dilatation (Figure 1B). Post-contrast T1W black blood arterial wall imaging illustrated avid enhancement and thickening of the distal supraclinoid internal carotid arterial walls bilaterally (Figure 1C). Cerebral spinal fluid (CSF) was obtained. While awaiting results of testing for viral CNS infections, the patient was treated with acyclovir, 30 mg/kg intravenous daily, and maintained on oral prednisolone, 2 mg/kg/day. The CSF at the time of diagnosis of vasculopathy contained 21 mononuclear cells and no red blood cells; protein was 39 mg/dL and glucose was 72 mg/dL. Quantitative PCR (Focus Diagnostics Reference Laboratory, Cypress, CA) amplified 7,116 copies of VZV DNA/mL in the CSF. To determine the VZV genotype, Forster Resonance Energy Transfer PCR was used to identify specific VZV DNA sequence polymorphisms within VZV open reading frames 38, 54, and 62, which distinguishes vaccine VZV from wild-type virus (Online Supplement Table 1) (3). This confirmed Oka varicella vaccine strain in the CSF. The CSF also contained anti-VZV IgG antibodies, but no antibodies to HSV-1 or HSV-2, enterovirus, cytomegalovirus, or Epstein-Barr virus were detected and the respective PCR analysis were similarly negative. The serum to CSF ratio of anti-VZV IgG antibody was markedly decreased (ratio 2.3) compared to albumin (ratio 149). Two weeks after treatment with acyclovir, the neurologic examination was completely normal, the CSF was acellular, and PCR was negative for VZV DNA. The patient received routine immunizations including VZV vaccination at 12 months of age. He had 3 episodes of vesicular rashes at ages 3, 4, and 5 years, which always occurred after completing a course of oral corticosteroids. The first rash tested positive for HSV. The second rash was identical. The third rash at age 5 years with vesicles on the lower thigh was diagnosed clinically as zoster. All rashes resolved on oral acyclovir. Past history included early-onset atopic dermatitis, food allergies often with anaphylaxis, biopsy-confirmed eosinophilic esophagitis, asthma and recurrent upper respiratory tract infections. Peripheral blood eosinophilia peaked at 9,000 eosinophils/μL and serum IgE at 472 IU/mL. During flares of respiratory or skin disease, he was treated with oral corticosteroids intermittently for 3 to 5 days, a few times annually. The frequency of such treatment increased and between ages 5½ and 6, he was treated with oral corticosteroids 1 to 2 times monthly during the prior 6 months. Conventional comparative genomic hybridization array analysis revealed a large deletion of exons 1 to 13 in a single allele of the DOCK8 gene. PCR analysis of genomic DNA and DOCK8 gene sequencing identified a single base pair mutation on the opposite allele at exon 12, resulting in a frame shift and premature stop codon: c.1266delC, p.Y423TfsX18, based upon reference sequence NM_00193536.1, isoform 3 (Figure 2A). Western Blot analysis confirmed lack of DOCK8 protein expression (Figure 2B). Parental testing demonstrated that the large exon deletion was inherited from the mother while the point mutation was inherited from the father. Immunological findings are summarized in Supplemental Table 2. Figure 2 DOCK8 molecular analyses The neurological symptoms and signs, imaging and CSF abnormalities, virological studies, and response to antiviral treatment were all features characteristically seen in VZV vasculopathy (4). Evidence of both focal and diffuse CNS disease was corroborated by widespread infarction produced by stenosis of multiple large cerebral arteries. The CSF examination revealed a pleocytosis as found in two-thirds of patients with VZV vasculopathy and both VZV DNA and anti-VZV IgG antibody with reduced serum/CSF ratios of anti-VZV IgG antibody were detected, indicative of intrathecal synthesis of anti-VZV IgG. Analysis of VZV DNA in CSF revealed that the VZV genotype was vaccine strain, demonstrating, for the first time, that VZV reactivation after vaccination in childhood can result in VZV vasculopathy. Although the underlying immunological consequences of DOCK8 deficiency remain to be fully elucidated, multiple immune system abnormalities may account for enhanced susceptibility to viral infection including impaired dendritic cell migration affecting T cell priming, lymphopenia, defective CD8 T cell activation and expansion, decreased production of the anti-viral cytokines IFN-γ and TNF-α, impaired T cell survival, decreased NK cell cytotoxicity, and antibody abnormalities (5-9). Germinal center formation and survival of germinal center B cells are impaired in DOCK8 deficiency, leading to defective long-lived antibody production (8). Responses to protein or polysaccharide-conjugated vaccines are often variable while responses to previously encountered viruses such as HSV and VZV have been normal as demonstrated here for VZV antibodies in serum and CSF. As in some other young patients with DOCK8 deficiency, this patient tended toward the milder spectrum of the disease with a relatively limited history of cutaneous infections, absence of severe systemic infections other than chronic mild otitis, and the modestly elevated serum IgE level. Instead, eosinophilia and moderate-severe eczema, asthma, and food sensitivities predominated. To control these conditions, courses of oral corticosteroids were administered with increased frequency over time. Interestingly, each of the 3 episodes of cutaneous viral infections with HSV or VZV was preceded by a course of oral corticosteroids. It is possible corticosteroids alone enabled the activation of vaccine strain VZV infection. More likely, the use of oral corticosteroids to gain disease control reduced the patient’s “immunologic threshold” and together resulted in reactivation of vaccine strain VZV and subsequent vasculopathy. In summary, a young patient with significant atopic disease and widespread infarction produced by stenosis of multiple large cerebral arteries was shown to express novel mutations on both alleles of the DOCK8 gene. For the first time, VZV vasculopathy was shown to be due to the vaccine strain. This case highlights the importance of considering the possibility of DOCK8 deficiency in the context of severe allergic disease and the potential risks for CNS infection including VZV vaccine-related vasculopathy.

SLAP Deficiency Enhances Number and Function of Regulatory T Cells Preventing Chronic Autoimmune Arthritis in SKG Mice

To test if manipulating TCR complex-mediated signaling (TCR signaling) could treat autoimmune disease, we generated the double SKG Src-like adapter protein (SLAP) knockout (DSSKO) mouse model. The SKG mutation in ZAP70 and SLAP have opposing functions on the regulation of TCR signaling. The combination of these two mutations alters TCR signaling in the context of a defined genetic background, uniform environmental conditions, and a well-characterized signaling disruption. In contrast to SKG mice, DSSKO mice do not develop zymosan-induced chronic autoimmune arthritis. This arthritis prevention is not due to significant alterations in thymocyte development or repertoire selection but instead enhanced numbers of regulatory T cells (Tregs) and decreased numbers of Th17 cells skewing the ratio of Tregs to autoreactive effector T cells. Treg depletion and/or functional blockade led to the development of arthritis in DSSKO mice. In vitro suppression of effector T cell proliferation was also enhanced, demonstrating that DSSKO mice have increased numbers of Tregs with increased function. Understanding how TCR signals influence development, expansion, and function of Tregs in DSSKO mice could advance our ability to manipulate Treg biology to treat ultimately autoimmune disease.

Choosing Wisely: The American College of Rheumatology's Top 5 for Pediatric Rheumatology

To create a pediatric rheumatology Top 5 list as part of the American Board of Internal Medicine Foundations Choosing Wisely campaign.