No abstract

IntroductionMigration of B cells into secondary lymphoid organs is required for an antigen-specific humoral immune response. B cells migrate from the bloodstream to lymph nodes by extravasation from high endothelial venules. The response to chemokines and integrinmediated adhesion to endothelial cells is a key step in this process. 1 B cells in secondary lymphoid organs are critical to homeostatic and inflammatory regulation of these tissues. If the lymph node becomes inflamed, B-cell migration is a prerequisite for normal hypertrophy and the further recruitment of dendritic and T cells. 2 B-cell trafficking within lymph nodes is also important during the generation of the germinal center reaction and humoral immune responses. [3][4][5][6] Abnormal chemoattractant-mediated B-cell migration is central to infiltration of malignant B cells into tissues and formation of ectopic germinal centers in autoimmune diseases. [7][8][9] The transduction of signals from cell surface receptors to the actin cytoskeleton to regulate cell adhesion and migration requires small G proteins of the Ras superfamily. [10][11][12] These include members of the Ras family, including Ras and Rap1, and members of the Rho family, such as Rac, Cdc42, and Rho. 13 Upstream activators of Rho proteins such as the Dbl homology domain proteins of the Vav family are required for ␤-integrin and chemokine-mediated Rac, Cdc42, and Rho activation and stable adhesions of cells. 14 Although B-cell migration is vital for their development, the pathways underlying integrin and chemokine signals in B cells are poorly defined. We identified the signaling protein SWAP-70 15 as required for B-cell migration and adhesion in vitro and in vivo. 16 Swap70 Ϫ/Ϫ B cells show aberrant integrin-mediated adhesion, defective polarization, and do not form uropods and stabilized lamellipodia in vitro. This leads to a defect in migration and homing of B cells to lymph nodes in vivo. In correlation with these defects in migration and adhesion, Swap70 Ϫ/Ϫ transitional B cells hyperadhere to the splenic red pulp and are impaired in differentiation into marginal zone B-cells. 17 In addition, Swap70 Ϫ/Ϫ B cells do not generate a normal germinal center response, 18 a process requiring high B-cell motility and a dynamic morphology, 6 which are most likely disturbed by the absence of SWAP-70.SWAP-70 interacts with and regulates proteins of the Rho family, in particular Rac and RhoA. 19,20 Unusually, SWAP-70 has a Dbl homology domain to the C-terminus of its pleckstrin homology (PH) domain. 20 The PH domain binds PIP 3 and SWAP-70 also binds F-but not G-actin. 20,21 The binding of SWAP-70 to F-actin depends on cell stimulation and is required for regulation of cytoskeletal rearrangements such as membrane ruffles. 21 Although its regulation of Rac and actin polymerization are likely to be important for SWAP-70's function in regulating B-cell migration, little is known about how SWAP-70 itself is regulated, other than its interaction with PIP 3 , which is required for its localization. ...

Objective. To describe a new kindred with Clq deficiency and to identify the molecular lesions responsible for complete functional Clq deficiency in this and 2 other previously described kindreds.Methods. The A-, B-, and C-chain genes of Clq were amplified by polymerase chain reaction, cloned, and sequenced. The DNA sequence was checked for mutations.

Asthma and allergies are major health concerns in which Ig isotype E plays a pivotal role. Ag-bound IgE drives mast cells and basophils into exocytosis, thereby promoting allergic and potentially anaphylactic reactions. The importance of tightly regulated IgE production is underscored by severe immunological conditions in humans with elevated IgE levels. Cytokines direct IgH class-switching to a particular isotype by initiation of germline transcription (GLT) from isotype-specific intronic (I) promoters. The switch to IgE depends on IL-4, which stimulates GLT of the Iε promoter, but is specifically and strongly impaired in Swap-70−/− mice. Although early events in IL-4 signal transduction (i.e., activation of the JAK/STAT6 pathway) do not require SWAP-70, SWAP-70 deficiency results in impaired Iε GLT. The affinity of STAT6 to chromatin is reduced in absence of SWAP-70. Chromatin immunoprecipitation revealed that SWAP-70 binds to Iε and is required for association of STAT6 with Iε. BCL6, known to antagonize STAT6 particularly at Iε, is increased on Iε in absence of SWAP-70. Other promoters bound by BCL6 and STAT6 were found unaffected. We conclude that SWAP-70 controls IgE production through regulation of the antagonistic STAT6 and BCL6 occupancy of Iε. The identification of this mechanism opens new avenues to inhibit allergic reactions triggered by IgE.

While the shelterin complex guards and coordinates the mechanism of telomere regulation, deregulation of this process is tightly linked to malignant transformation and cancer. Here, we present the novel finding of a germline stop-gain variant (p.Q199*) in the shelterin complex gene POT1, which was identified in a child with acute myeloid leukemia. We show that the cells overexpressing the mutated POT1 display increased DNA damage and chromosomal instabilities compared to the wildtype counterpart. Protein and mRNA expression analyses in the primary patient cells further confirm that, physiologically, the variant leads to a nonfunctional POT1 allele in the patient. Subsequent telomere length measurements in the primary cells carrying heterozygous POT1 p.Q199* as well as POT1 knockdown AML cells revealed telomeric elongation as the main functional effect. These results show a connection between POT1 p.Q199* and telomeric dysregulation and highlight POT1 germline deficiency as a predisposition to myeloid malignancies in childhood.