Lack of IL-17 Receptor A signaling aggravates lymphoproliferation in C57BL/6 lpr mice.

Defects in Fas function correlate with susceptibility to systemic autoimmune diseases like autoimmune lymphoproliferative syndrome (ALPS) and systemic lupus erythematosus (SLE). C57BL/6 lpr (B6/lpr) mice are used as an animal model of ALPS and develop a mild SLE phenotype. Involvement of interleukin-17A (IL-17A) has been suggested in both phenotypes. Since IL-17 receptor A is part of the signaling pathway of many IL-17 family members we investigated the role of IL-17 receptor signaling in disease development in mice with a B6/lpr background. B6/lpr mice were crossed with IL-17 receptor A deficient (IL-17RA KO) mice and followed over time for disease development. IL-17RA KO/lpr mice presented with significantly enhanced lymphoproliferation compared with B6/lpr mice, which was characterized by dramatic lymphadenomegaly/splenomegaly and increased lymphocyte numbers, expansion of double-negative (DN) T-cells and enhanced plasma cell formation. However, the SLE phenotype was not enhanced, as anti-nuclear antibody (ANA) titers and induction of glomerulonephritis were not different. In contrast, levels of High Mobility Group Box 1 (HMGB1) and anti-HMGB1 autoantibodies were significantly increased in IL-17RA KO/lpr mice compared to B6/lpr mice. These data show that lack of IL-17RA signaling aggravates the lymphoproliferative phenotype in B6/lpr mice but does not affect the SLE phenotype.

Impact of Aging on the Frequency, Phenotype, and Function of CD161-Expressing T Cells.

Immune-aging is associated with perturbed immune responses in the elderly. CD161-expressing T cells, i.e., the previously described subsets of CD161+ CD4+ T cells, CD161high CD8+ T cells, and CD161int CD8+ T cells, are highly functional, pro-inflammatory T cells. These CD161-expressing T cells are critical in immunity against microbes, while possibly contributing to autoimmune diseases. So far, little is known about the impact of aging on the frequency, phenotype, and function of these CD161-expressing T cells. In the current study, we investigated the impact of aging on CD161+ CD4+ T cells, CD161high CD8+ T cells, and CD161int CD8+ T cells in peripheral blood samples of 96 healthy subjects (age 20-84). Frequencies of CD161+ CD4+ T cells and CD161int CD8+ T cells were stable with aging, whereas frequencies of CD161high CD8+ T cells declined. Although CD161high CD8+ T cells were mostly T cell receptor-Vα7.2+ mucosal-associated invariant T cells, CD161 expressing CD4+ and CD8+ T cells showed a limited expression of markers for gamma-delta T cells or invariant natural killer (NK) T cells, in both young and old subjects. In essence, CD161-expressing T cells showed a similar memory phenotype in young and old subjects. The expression of the inhibitory NK receptor KLRG1 was decreased on CD161+ CD4+ T cells of old subjects, whereas the expression of other NK receptors by CD161-expressing T cells was unaltered with age. The expression of cytotoxic effector molecules was similar in CD161high and CD161int CD8+ T cells of young and old subjects. The ability to produce pro-inflammatory cytokines was preserved in CD161high and CD161int CD8+ T cells of old subjects. However, the percentages of IFN-γ+ and interleukin-17+ cells were significantly lower in CD161+ CD4+ T cells of old individuals than those of young individuals. In addition, aging was associated with a decrease of nonclassic T helper 1 cells, as indicated by decreased percentages of CD161-expressing cells within the IFN-γ+ CD4+ T cell compartment of old subjects. Taken together, aging is associated with a numerical decline of circulating CD161high CD8+ T cells, as well as a decreased production of pro-inflammatory cytokines by CD161+ CD4+ T cells. These aging-associated changes could contribute to perturbed immunity in the elderly.

High mobility group box 1 skews macrophage polarization and negatively influences phagocytosis of apoptotic cells.

OBJECTIVES: Decreased phagocytosis of apoptotic cells plays an important role in the pathogenesis of SLE. This can lead to secondary necrosis and release of nuclear proteins, such as high mobility group box 1 (HMGB1). We hypothesized that increased HMGB1 levels, as present in SLE, skew macrophage differentiation towards M1-like phenotypes and thereby diminish uptake of apoptotic cells. The aim of this study was to investigate the effect of HMGB1 on macrophage polarization and on phagocytic capacity of differentiated macrophages. METHODS: SLE patients with quiescent disease (SLEDAI ⩽4) and healthy controls (HCs) were included. Monocytes and differentiated M1 and M2 macrophages were assessed for expression of M1 and M2 markers and for phagocytic capacity. HMGB1 was added during differentiation and during phagocytosis. RESULTS: Expression of CD86 (M1) was not different, whereas CD163 (M2) was significantly lower on SLE monocytes. After differentiation, no differences regarding surface receptor expression and phagocytic capacity were observed between M1 and M2 macrophages from SLE patients and HCs. Addition of HMGB1 during M2 differentiation resulted in high IL-6 and TNF-α mRNA expression and reduced phagocytic capacity of apoptotic cells. Furthermore, adding HMGB1 to apoptotic Jurkat cells diminished phagocytosis of these cells. CONCLUSION: Circulating monocytes from SLE patients display an M1-like phenotype compared with HCs, but in vitro differentiation abolishes this difference. HMGB1 skews differentiation of M2-like macrophages towards an M1-like phenotype and, subsequently, reduces phagocytosis of apoptotic cells. These data imply that the phenotype of monocytes or macrophages is determined by their environment, such as the presence of cytokines and HMGB1.

Treatment with Anti-HMGB1 Monoclonal Antibody Does Not Affect Lupus Nephritis in MRL/lpr Mice.

High mobility group box 1 (HMGB1) is a nuclear DNA binding protein that acts as an alarmin when secreted. HMGB1 is increased in systemic lupus erythematosus and might represent a potential therapeutic target. We investigated whether treatment with an anti-HMGB1 antibody affects the development of lupus nephritis in MRL/lpr mice. Seven-week-old MRL/lpr mice were injected intraperitoneally twice weekly for 10 wks with 50 µg monoclonal anti-HMGB1 (2G7, mouse IgG2b) (n = 12) or control antibody (n = 11). Control MRL/MPJ mice (n = 10) were left untreated. Every 2 wks, blood was drawn and urine was collected at wk 7, 11 and 17. Mice were sacrificed at 17 wks for complete disease evaluation. Plasma HMGB1 and anti-HMGB1 levels were increased in MRL/lpr mice compared with control MRL/MPJ mice. There were no differences in albuminuria, urine HMGB1 and plasma levels of complement C3, anti-dsDNA and proinflammatory cytokines between untreated and treated mice at any time point. Lupus nephritis of mice treated with anti-HMGB1 monoclonal antibody (mAb) was classified as class III (n = 3) and class IV (n = 9), while mice treated with control mAb were classified as class II (n = 4), class III (n = 2) and class IV (n = 5). IgG and C3 deposits in kidneys were similar in mice treated with anti-HMGB1 mAb or control mAb. In conclusion, treatment with monoclonal anti-HMGB-1 antibody 2G7 does not affect development of lupus nephritis, disease progression or proinflammatory cytokine levels in MRL/lpr mice. This result indicates that blocking of HMGB1 by this neutralizing antibody does not affect lupus nephritis in MRL/lpr mice.

Aging-dependent decline of IL-10 producing B cells coincides with production of antinuclear antibodies but not rheumatoid factors.

Aging is associated with development of autoimmunity. Loss of B cell tolerance in the elderly is suggested by an increased prevalence of anti-nuclear antibodies (ANAs) and rheumatoid factors (RFs). Accumulating evidence indicates that B cells also impact autoimmunity via secretion of cytokines. So far, few studies have directly assessed the effect of aging on the latter B cell function. Here, we determined if and how human aging influences the production of cytokines by B cells. In a cross-sectional study, we found that absolute numbers of circulating B cells were similar in 31 young (ages 19-39) and 73 old (age ≥ 60) individuals. Numbers of transitional B cells (CD19(+)CD27(-)CD38(High)CD24(High)) were decreased in old individuals, whereas numbers of naive and memory B cell subsets were comparable in young and old individuals. Short-term in vitro stimulation of whole blood samples revealed that numbers of B cells capable of producing TNF-α were similar in young and old individuals. In contrast, B cells capable of IL-10 production were decreased in old subjects. This decline of IL-10(+) B cells was observed in old individuals that were ANA positive, and in those that were negative for both ANAs and RFs. However, IL-10(+) B cells were remarkably well retained in the circulation of old subjects that were RF positive. Thus, pro-inflammatory TNF-α(+) B cells are retained in the elderly, whereas IL-10(+) B cells generally decline. In addition, our findings indicate that IL-10(+) B cells may differentially impact the development of ANAs and RFs in the elderly.

Low-affinity TCR engagement drives IL-2-dependent post-thymic maintenance of naive CD4+ T cells in aged humans.

Insight into the maintenance of naive T cells is essential to understand defective immune responses in the context of aging and other immune compromised states. In humans, naive CD4+ T cells, in contrast to CD8+ T cells, are remarkably well retained with aging. Here, we show that low-affinity TCR engagement is the main driving force behind the emergence and accumulation of naive-like CD4+ T cells with enhanced sensitivity to IL-2 in aged humans. In vitro, we show that these CD45RA(+) CD25(dim) CD4(+) T cells can develop from conventional naive CD25(-) CD4+ T cells upon CD3 cross-linking alone, in the absence of costimulation, rather than via stimulation by the homeostatic cytokines IL-2, IL-7, or IL-15. In vivo, TCR engagement likely occurs in secondary lymphoid organs as these cells were detected in lymph nodes and spleen where they showed signs of recent activation. CD45RA(+) CD25(dim) CD4+ T cells expressed a broad TCRVß repertoire and could readily differentiate into functional T helper cells. Strikingly, no expansion of CD45RA(+) CD25(dim) CD8+ T cells was detected with aging, thereby implying that maintenance of naive CD4+ T cells is uniquely regulated. Our data provide novel insight into the homeostasis of naive T cells and may guide the development of therapies to preserve or restore immunity in the elderly.

Quantifying Distribution of Flow Cytometric TCR-Vß Usage with Economic Statistics.

Measuring changes of the T cell receptor (TCR) repertoire is important to many fields of medicine. Flow cytometry is a popular technique to study the TCR repertoire, as it quickly provides insight into the TCR-Vß usage among well-defined populations of T cells. However, the interpretation of the flow cytometric data remains difficult, and subtle TCR repertoire changes may go undetected. Here, we introduce a novel means for analyzing the flow cytometric data on TCR-Vß usage. By applying economic statistics, we calculated the Gini-TCR skewing index from the flow cytometric TCR-Vß analysis. The Gini-TCR skewing index, which is a direct measure of TCR-Vß distribution among T cells, allowed us to track subtle changes of the TCR repertoire among distinct populations of T cells. Application of the Gini-TCR skewing index to the flow cytometric TCR-Vß analysis will greatly help to gain better understanding of the TCR repertoire in health and disease.

Serum markers associated with disease activity in giant cell arteritis and polymyalgia rheumatica.

OBJECTIVE: To compare multiple serum markers for their ability to detect active disease in patients with GCA and in those with PMR. METHODS: Twenty-six markers related to immune cells that may be involved in GCA and PMR were determined by ELISA and multiplex assay in the serum of 24 newly diagnosed, untreated GCA/PMR patients, 14 corticosteroid (CS)-treated GCA/PMR patients in remission and 13 healthy controls. Receiver operating characteristic analysis with area under the curve and Spearman's correlation coefficients were performed. RESULTS: Serum B-cell activating factor (BAFF), CXCL9 and IL-6 were increased in newly diagnosed GCA and PMR patients. Serum CCL2, CCL11, IL-10 and sIL-2R were modulated in GCA patients only and CXCL10 in PMR patients only. BAFF, CXCL9 and IL-6 accurately distinguished newly diagnosed GCA and PMR patients from healthy controls, as shown by area under the curve > 0.80. Upon CS-induced remission, serum BAFF and IL-6 decreased significantly in both GCA and PMR patients, whereas CXCL9 remained high. Serum BAFF and IL-6 correlated strongly with ESR and CRP in GCA and PMR patients. CONCLUSION: Among the serum markers tested, BAFF and IL-6 showed the strongest association with disease activity in both GCA and PMR patients. The diagnostic value of these markers should be evaluated in larger, longitudinal studies with GCA and PMR patients, and in patients with infections or other inflammatory conditions.

Aging disturbs the balance between effector and regulatory CD4+ T cells.

Healthy aging requires an optimal balance between pro-inflammatory and anti-inflammatory immune responses. Although CD4+ T cells play an essential role in many immune responses, few studies have directly assessed the effect of aging on the balance between effector T (Teff) cells and regulatory T (Treg) cells. Here, we determined if and how aging affects the ratio between Treg and Teff cells. Percentages of both naive Treg (nTreg; CD45RA+CD25(int)FOXP3(low)) and memory Treg (memTreg; CD45RA-CD25(high)FOXP3(high)) cells were determined by flow cytometry in peripheral blood samples of healthy individuals of various ages (20-84 years). Circulating Th1, Th2 and Th17 effector cells were identified by intracellular staining for IFN-γ, IL-4 and IL-17, respectively, upon in vitro stimulation with PMA and calcium ionophore. Whereas proportions of nTreg cells declined with age, memTreg cells increased. Both Th1 and Th2 cells were largely maintained in the circulation of aged humans, whereas Th17 cells were decreased. Similar to memTreg cells, the 3 Teff subsets resided primarily in the memory CD4+ T cell compartment. Overall, Treg/Teff ratios were increased in the memory CD4+ T cell compartment of aged individuals when compared to that of young individuals. Finally, the relative increase of memTreg cells in elderly individuals was associated with poor responses to influenza vaccination. Taken together, our findings imply that aging disturbs the balance between Treg cells and Teff cells.

Altered cellular and humoral immunity to varicella-zoster virus in patients with autoimmune diseases.

OBJECTIVE: Patients with autoimmune diseases such as systemic lupus erythematosus (SLE) and granulomatosis with polyangiitis (Wegener's) (GPA) have a 3-20-fold increased risk of herpes zoster compared to the general population. The aim of this study was to evaluate if susceptibility is due to decreased levels of cellular and/or humoral immunity to the varicella-zoster virus (VZV). METHODS: A cross-sectional study of VZV-specific immunity was performed in 38 SLE patients, 33 GPA patients, and 51 healthy controls. Levels of IgG and IgM antibodies to VZV were measured using an in-house glycoprotein enzyme-linked immunosorbent assay (ELISA). Cellular responses to VZV were determined by interferon-γ (IFNγ) enzyme-linked immunospot (ELISpot) assay and carboxyfluorescein succinimidyl ester (CFSE) dye dilution proliferation assay. RESULTS: Levels of IgG antibodies to VZV were increased in SLE patients as compared to healthy controls, but levels of IgM antibodies to VZV were not. Antibody levels in GPA patients did not differ significantly from levels in healthy controls. In response to stimulation with VZV, decreased numbers of IFNγ spot-forming cells were found among SLE patients (although not GPA patients) as compared to healthy controls. Proliferation of CD4+ T cells in response to stimulation with VZV was decreased in SLE patients but not GPA patients. CONCLUSION: SLE patients have increased levels of IgG antibodies against VZV, while cellular immunity is decreased. In GPA patients, antibody levels as well as cellular responses to VZV were comparable to those in healthy controls. These data suggest that increased prevalence of herpes zoster in SLE patients is due to a poor cellular response. Vaccination strategies should aim to boost cellular immunity against VZV.

Disturbed B cell homeostasis in newly diagnosed giant cell arteritis and polymyalgia rheumatica.

OBJECTIVE: Several lines of evidence indicate that B cells may be involved in the immunopathology of giant cell arteritis (GCA) and polymyalgia rheumatica (PMR). This study was undertaken to examine the distribution of defined B cell subsets, including effector B (Beff) cells and regulatory B (Breg) cells, in patients with GCA and patients with PMR before and after corticosteroid treatment. METHODS: Circulating B cells were analyzed in 34 newly diagnosed, untreated patients with GCA or PMR, and in 44 followup samples from patients with GCA or PMR who received corticosteroids for 2 weeks or 3 months. For comparison, 40 age-matched healthy controls and 11 rheumatoid arthritis (RA) patients were included. Serum BAFF levels were determined, and temporal arteries were studied by immunohistochemistry. RESULTS: Patients newly diagnosed as having GCA or PMR, but not patients with RA, had decreased numbers of circulating B cells compared to healthy controls. B cell numbers recovered rapidly in treated patients with GCA and PMR in remission. This recovery was not achieved by compensatory hyperproliferation or enhanced bone marrow production. B cell numbers inversely correlated with erythrocyte sedimentation rates, C-reactive protein levels, and serum BAFF levels. Tumor necrosis factor α-positive Beff cells, but not interleukin-10 (IL-10)-positive Breg cells, were decreased in patients newly diagnosed as having GCA or PMR. Following treatment, circulating numbers of Beff cells normalized. The returning Beff cells demonstrated an enhanced capacity to produce IL-6. Few B cells were found in temporal artery biopsy specimens from GCA patients. CONCLUSION: We show for the first time that the distribution of B cells is highly disturbed in GCA and PMR and that B cells likely contribute to the enhanced IL-6 response in both diseases.

Epithelial and dendritic cells in the thymic medulla promote CD4+Foxp3+ regulatory T cell development via the CD27-CD70 pathway.

CD4(+)Foxp3(+) regulatory T cells (Treg cells) are largely autoreactive yet escape clonal deletion in the thymus. We demonstrate here that CD27-CD70 co-stimulation in the thymus rescues developing Treg cells from apoptosis and thereby promotes Treg cell generation. Genetic ablation of CD27 or its ligand CD70 reduced Treg cell numbers in the thymus and peripheral lymphoid organs, whereas it did not alter conventional CD4(+)Foxp3(-) T cell numbers. The CD27-CD70 pathway was not required for pre-Treg cell generation, Foxp3 induction, or mature Treg cell function. Rather, CD27 signaling enhanced positive selection of Treg cells within the thymus in a cell-intrinsic manner. CD27 signals promoted the survival of thymic Treg cells by inhibiting the mitochondrial apoptosis pathway. CD70 was expressed on Aire(-) and Aire(+) medullary thymic epithelial cells (mTECs) and on dendritic cells (DCs) in the thymic medulla. CD70 on both mTECs and DCs contributed to Treg cell development as shown in BM chimera experiments with CD70-deficient mice. In vitro experiments indicated that CD70 on the CD8α(+) subset of thymic DCs promoted Treg cell development. Our data suggest that mTECs and DCs form dedicated niches in the thymic medulla, in which CD27-CD70 co-stimulation rescues developing Treg cells from apoptosis, subsequent to Foxp3 induction by TCR and CD28 signals.

The CD27 and CD70 costimulatory pathway inhibits effector function of T helper 17 cells and attenuates associated autoimmunity.

T helper 17 (Th17) cells protect against infection but also promote inflammation and autoimmunity. Therefore, the factors that govern Th17 cell differentiation are of special interest. The CD27 and CD70 costimulatory pathway impeded Th17 effector cell differentiation and associated autoimmunity in a mouse model of multiple sclerosis. CD27 or CD70 deficiency exacerbated disease, whereas constitutive CD27 signaling strongly reduced disease incidence and severity. CD27 signaling did not impact master regulators of T helper cell lineage commitment but selectively repressed transcription of the key effector molecules interleukin-17 (IL-17) and the chemokine receptor CCR6 in differentiating Th17 cells. CD27 mediated this repression at least in part via the c-Jun N-terminal kinase (JNK) pathway that restrained IL-17 and CCR6 expression in differentiating Th17 cells. CD27 signaling also resulted in epigenetic silencing of the Il17a gene. Thus, CD27 costimulation via JNK signaling, transcriptional, and epigenetic effects suppresses Th17 effector cell function and associated pathological consequences.

Cell-mediated immune responses to inactivated trivalent influenza-vaccination are decreased in patients with common variable immunodeficiency.

Influenza-specific cell-mediated immune (CMI) responses can protect from influenza, but may be decreased in CVID-patients since defects in CMI responses have been demonstrated in CVID-patients. Therefore CMI responses were evaluated in 15 CVID-patients and 15 matched healthy controls (HC) by determining frequencies of interferon (IFN)γ-producing PBMC, and frequencies of IFNγ-, interleukin (IL)-2- and tumour necrosis factor (TNF)α-producing CD4+ and CD8+ T-cells before and after influenza vaccination using IFNγ enzyme-linked immunospot (IFNγ-ELISpot) and flow cytometry. Humoral responses were determined using haemagglutination inhibition assay. In CVID-patients the number of spotforming PBMC in the IFNγ-ELISpot did not increase following influenza vaccination, in contrast to HC. In flow cytometry, the frequencies of IFNγ-producing T-cells decreased in CVID-patients after influenza vaccination, while in HC the frequencies of IFNγ-production flow cytometry increased. Concluding, CMI responses following influenza vaccination are hampered in CVID-patients compared to HC. Additional protective strategies against influenza other than vaccination are warranted.

The invariant chain transports TNF family member CD70 to MHC class II compartments in dendritic cells.

CD70 is a TNF-related transmembrane molecule expressed by mature dendritic cells (DCs), which present antigens to T cells via major histocompatibility complex (MHC) molecules. In DCs, CD70 localizes with MHC class II molecules in late endosomal vesicles, known as MHC class II compartments (MIICs). MIICs are transported to the immune synapse when a DC contacts an antigen-specific CD4(+) T cell. Consequently, MHC class II and CD70 are simultaneously exposed to the T cell. Thereby, T-cell activation via the antigen receptor and CD70-mediated co-stimulation are synchronized, apparently to optimize the proliferative response. We report here that the invariant chain (Ii), a chaperone known to transport MHC class II to MIICs, performs a similar function for CD70. CD70 was found to travel by default to the plasma membrane, whereas Ii coexpression directed it to late endosomes and/or lysosomes. In cells containing the MHC class II presentation pathway, CD70 localized to MIICs. This localization relied on Ii, since transport of CD70 from the Golgi to MIICs was impeded in Ii-deficient DCs. Biophysical and biochemical studies revealed that CD70 and Ii participate in an MHC-class-II-independent complex. Thus, Ii supports transport of both MHC class II and CD70 to MIICs and thereby coordinates their delivery to CD4(+) T cells.

Opsonization of late apoptotic cells by systemic lupus erythematosus autoantibodies inhibits their uptake via an Fcgamma receptor-dependent mechanism.

OBJECTIVE: Decreased clearance of apoptotic cells is suggested to be a major pathogenic factor in systemic lupus erythematosus (SLE). The aim of this study was to investigate whether the binding of SLE autoantibodies to apoptotic cells influences the phagocytosis of these cells by macrophages. METHODS: Apoptosis was induced in a human T cell line (Jurkat) and a keratinocyte cell line (HaCaT) by ultraviolet B irradiation. Binding of purified IgG from 26 SLE patients and 15 healthy controls to apoptotic cells was assessed by flow cytometry and Western blotting. Phagocytosis of IgG-opsonized apoptotic cells by monocyte-derived macrophages was assessed by light microscopy. Similar experiments were performed with a monoclonal antibody against SSA/Ro and IgG fractions from 5 patients with Sjögren's syndrome (SS) and 5 patients with rheumatoid arthritis (RA). RESULTS: IgG fractions from all 26 SLE patients bound to late apoptotic, but not early apoptotic, cells. IgG fractions isolated from SLE patients with different autoantibody profiles showed comparable levels of binding. IgG fractions from healthy controls did not bind. Opsonization of apoptotic cells with IgG fractions from SLE patients resulted in a significant inhibition of phagocytosis as compared with healthy control IgG fractions. A monoclonal antibody directed against SSA/Ro and IgG isolated from 5 antinuclear antibody (ANA)-positive patients with SS were also able to elicit these effects, whereas IgG from 5 ANA-negative patients with RA did not. The inhibitory effect of patient IgG was abolished by blocking either the Fcgamma receptors (FcgammaR) or the constant region of IgG, using a specific Fc-blocking peptide. CONCLUSION: Autoantibodies from SLE patients are able to opsonize apoptotic cells and inhibit their uptake by macrophages via an FcgammaR-dependent mechanism.

Ubiquitin ligase activity of c-Cbl guides the epidermal growth factor receptor into clathrin-coated pits by two distinct modes of Eps15 recruitment.

We have demonstrated previously that c-Cbl requires the presence of a functional ubiquitin interacting motif (UIM) in Eps15 to mediate epidermal growth factor receptor (EGFR) endocytosis. Both the ubiquitin ligase activity of c-Cbl and the UIM of Eps15 were necessary for plasma membrane recruitment of Eps15 and entry of ligand-bound EGFR into coated pits and vesicles containing Eps15. This is consistent with a scenario in which ubiquitin moieties appended to activated EGFR complexes act as docking sites for Eps15 and thereby recruit receptors into clathrin coated pits. Here, we have investigated which additional structural features of c-Cbl are required for this process. We find that c-Cbl can guide ligand-bound EGFR into the Eps15 internalization route by two distinct mechanisms. These are either dependent on the phosphotyrosine binding domain of c-Cbl that directly binds to the EGFR or on the region C-terminal of the Ring finger, which allows for indirect binding to an alternative site on the receptor. No strict requirement exists for either ubiquitin modified EGFR or the Cbl binding ubiquitination substrate CIN85 as docking site for the UIM of Eps15. Only in the phosphotyrosine binding-dependent pathway, the EGFR is ubiquitinated and may serve as a site of recruitment for Eps15. Only in this pathway, Eps15 is tyrosine-phosphorylated, but this appears unrelated to its capacity to participate in EGFR internalization.

c-Cbl directs EGF receptors into an endocytic pathway that involves the ubiquitin-interacting motif of Eps15.

c-Cbl associates with the activated EGF receptor before endocytosis. We here reveal that the capacity of c-Cbl to promote receptor internalization depends on its ubiquitin ligase activity, which functionally connects the EGF receptor to Eps15, a mediator of clathrin-coated pit formation. EGF-induced phosphorylation of Eps15, as well as recruitment of Eps15 to the plasma membrane and its co-localization with the EGF receptor in endosomes required the ubiquitin ligase activity of c-Cbl. This suggested that ubiquitin provides a direct or indirect link between the receptor and Eps15. Indeed, EGF-induced redistribution of Eps15 to the plasma membrane and endosomes depended on its ubiquitin-interacting motif. Upon over-expression, the ubiquitin-interacting motif abrogated the capacity of c-Cbl to promote EGF receptor endocytosis and only allowed receptor internalization via a route that lacked Eps15. Our findings disclose a novel function for the c-Cbl ubiquitin ligase and identify ubiquitin as a module that directs the EGF receptor into an endocytic pathway involving Eps15.

Increased seroreactivity in tic disorder patients to a 60 kDa protein band from a neuronal cell line.

In tic disorders, increased seroreactivity against neuronal antigens has been demonstrated, without performing molecular characterization of antigens. Here, unselected patients with a tic disorder were compared with healthy controls, autistic disorder (AD), and obsessive-compulsive disorder (OCD) patients. Seroreactivity against neuroblastoma cells was analyzed by Western blot. Anti-60 kDa binding occurred significantly more frequently in tic disorder patients (67.1%) than in AD (40.0%), OCD (40.0%) and healthy controls (41.9%). Sequence analysis of the 60 kDa protein band identified this as a ubiquitous heat shock protein. However, the involvement of other autoantigens with a molecular weight of 60 kDa cannot be excluded.

Serum amyloid P component binds to late apoptotic cells and mediates their uptake by monocyte-derived macrophages.

OBJECTIVE: Some pentraxins, such as C-reactive protein, bind to apoptotic cells and are involved in the clearance of these cells. We undertook this study to determine whether serum amyloid P component (SAP; a pentraxin that, when deficient in mice, results in lupus-like disease) binds to apoptotic cells and to assess the functional consequences of SAP binding for their phagocytosis by macrophages. METHODS: Human peripheral blood monocytes were isolated and cultured for 7 days to obtain monocyte-derived macrophages. Jurkat cells were irradiated with ultraviolet B to induce apoptosis. After 4 hours, a mean +/- SEM of 54.0 +/- 5.1% of these cells stained with annexin V and were propidium iodide negative (early apoptotic [EA] cells). After 24 hours, 77.3 +/- 2.7% of cells stained positive with both annexin V and propidium iodide (late apoptotic [LA] cells or secondary necrotic cells). EA and LA cells were incubated with fluorescein isothiocyanate-labeled SAP in the presence or absence of Ca(2+), and binding was measured by flow cytometry. Phagocytosis was tested by incubation of macrophages with EA or LA cells in the presence of normal human serum (NHS) and quantified as a phagocytosis index (PI; number of Jurkat cells internalized by 100 macrophages). Experiments were repeated with SAP-depleted serum and after reconstitution with increasing concentrations of SAP. RESULTS: The majority of LA cells did bind SAP in the presence of Ca(2+), whereas EA cells did not. SAP depletion of NHS resulted in a 50% decrease in the PI for LA cells, and complete restoration of the PI could be demonstrated with SAP reconstitution up to 100 microg/ml. SAP depletion had no effect on phagocytosis of EA cells. CONCLUSION: SAP binds to LA cells and is involved in the phagocytosis of these cells by human monocyte-derived macrophages. This may have consequences for diseases such as systemic lupus erythematosus, in which phagocytosis of apoptotic cells is decreased.