The adaptor protein Bam32 in human dendritic cells participates in the regulation of MHC class I-induced CD8+ T cell activation.

The B lymphocyte adaptor molecule of 32 kDa (Bam32) is strongly induced during the maturation of dendritic cells (DC). Most known functions of Bam32 are related to the signaling of the B cell receptor for Ag. Because DC do not express receptors specific for Ags, we aim at characterizing the role of Bam32 in human monocyte-derived DC in this study. Our results show that binding of allogeneic T cells to mature DC causes accumulation of Bam32 on the contact sites and that this translocation is mimicked by Ab-mediated engagement of MHC class I. Silencing of Bam32 in mature monocyte-derived DC results in an enhanced proliferation of CD8(+) T cells in an Ag-specific T cell proliferation assay. Further studies identify galectin-1 as an intracellular binding partner of Bam32. Regulating immune responses via regulatory T cell (Treg) modulation is one of the many immunological activities attributed to galectin-1. Therefore, we assayed mixed leukocyte reactions for Treg expansion and found fewer Treg in reactions stimulated with DC silenced for Bam32 compared to reactions stimulated with DC treated with a nontarget control. Based on our findings, we propose a role for Bam32 in the signaling of MHC class I molecules in professional Ag-presenting DC for the regulation of CD8(+) T cell activation. It is distinct from that of MHC class I recognized by CD8(+) T cells leading to target [corrected] cell death. Thus, our data pinpoint a novel level of T cell regulation that may be of biological relevance.

In human monocyte derived dendritic cells SOCS1 interacting with CYTIP induces the degradation of CYTIP by the proteasome.

CYTIP (cytohesin interacting protein) is an intracellular molecule induced in dendritic cells during maturation. CYTIP modulates the binding intensity of the adhesion molecule LFA-1. If dendritic cells are silenced for CYTIP they keep longer contacts with T-cells resulting in a lower T cell stimulation. We identified Suppressor of cytokine signaling-1 (SOCS-1) as a binding partner for CYTIP in human monocyte derived dendritic cells. In Western blot analyses we found that CYTIP expression is down regulated at later time points, starting at about 72 hours after induction of maturation. To investigate a possible role for SOCS-1 in taking CYTIP to the degradation machinery of the cell we measured endogenous CYTIP protein levels in mature dendritic cells transfected with SOCS-1 encoding plasmid in quantitative Western blot analyses. We observed lower amounts of endogenous CYTIP in mature dendritic cells transfected with SOCS-1 encoding plasmid compared with untransfected dendritic cells. Experiments with the proteasome-inhibitor Bortezomib/Velcade® show stable CYTIP expression levels in dendritic cells. In addition, we show that CYTIP in dendritic cells matured for 48 hours is ubiquitinated and thus ready for degradation. We here describe a newly identified binding partner of CYTIP, SOCS-1, and confirm its function in regulating the degradation of CYTIP by the proteasome.

Lower prevalence of common filaggrin mutations in a community sample of atopic eczema: is disease severity important?

BACKGROUND: Recent studies have shown an association of loss-of-function mutations in the filaggrin gene (FLG) with ichthyosis vulgaris and atopic eczema (AE). Case selection may have distorted the hitherto reported prevalence of FLG mutations and their relation to atopic disease. The aim of the study was to determine the true population prevalence of FLG mutations in unselected children with and without reported physician diagnoses of asthma, allergic rhinitis and AE and their relationship with family history of atopic disease. METHODS: We used a nested case-control design by sampling children with reported doctor's diagnoses of AE, asthma and allergic rhinitis and randomly selected controls from a larger cross-sectional study (n = 1263). Most common FLG mutations R501X, 2282del4, and R2447X were screened in DNA extracted from defrosted urine samples. The relationship of the combined FLG variants with atopic diseases and with reported family history of AE, asthma, and rhinitis was assessed. RESULTS: In the patient group one homozygote (R501X/R501X), 4 compound heterozygotes (3 R501X/2282del4, one 2282del4/R2447X), and 17 heterozygotes (10 R501X/wt, 5 2282del4/wt, and 2 R2447X/wt), in the control group 9 heterozygotes (5 R501X/wt, 4 2282del4/wt) were detected. The combined prevalence of FLG loss-of-function alleles was 5% in the control group and 9% in the atopic sample. In a subgroup analysis, the combination of allergic rhinitis and AE showed a significant relationship with FLG mutations, OR = 3.7 (1.01-12.67, p = 0.024). Likewise, significant relations with reported family history of asthma, OR = 4.35 (1.78-10.62, p = 0.0012), allergic rhinitis, OR = 2.33 (1.49-3.63, p = 0.0002), and AE, OR = 5.08 (2.78-9.30, p ≤ 0.0001) were observed. In contrast to clinical studies with higher percentages of severely affected persons, FLG mutations here showed a moderate association with atopic disease. CONCLUSIONS: Case selection may be responsible for overestimating the prevalence of FLG mutations in atopic disease.