B cells require DOCK8 to elicit and integrate T cell help when antigen is limiting.

Dedicator of cytokinesis 8 (DOCK8) immunodeficiency syndrome is characterized by a failure of the germinal center response, a process involving the proliferation and positive selection of antigen-specific B cells. Here, we describe how DOCK8-deficient B cells are blocked at a light-zone checkpoint in the germinal centers of immunized mice, where they are unable to respond to T cell-dependent survival and selection signals and consequently differentiate into plasma cells or memory B cells. Although DOCK8-deficient B cells can acquire and present antigen to initiate activation of cognate T cells, integrin up-regulation, B cell-T cell conjugate formation, and costimulation are insufficient for sustained B cell and T cell activation when antigen availability is limited. Our findings provide an explanation for the failure of the humoral response in DOCK8 immunodeficiency syndrome and insight into how the level of available antigen modulates B cell-T cell cross-talk to fine-tune humoral immune responses and immunological memory.

Regulatory T-cell dysfunction and cutaneous exposure to Staphylococcus aureus underlie eczema in DOCK8 deficiency.

BACKGROUND: Dedicator of cytokinesis 8 (DOCK8)-deficient patients have severe eczema, elevated IgE, and eosinophilia, features of atopic dermatitis (AD). OBJECTIVE: We sought to understand the mechanisms of eczema in DOCK8 deficiency. METHODS: Skin biopsy samples were characterized by histology, immunofluorescence microscopy, and gene expression. Skin barrier function was measured by transepidermal water loss. Allergic skin inflammation was elicited in mice by epicutaneous sensitization with ovalbumin (OVA) or cutaneous application of Staphylococcus aureus. RESULTS: Skin lesions of DOCK8-deficient patients exhibited type 2 inflammation, and the patients' skin was colonized by Saureus, as in AD. Unlike in AD, DOCK8-deficient patients had a reduced FOXP3:CD4 ratio in their skin lesions, and their skin barrier function was intrinsically intact. Dock8-/- mice exhibited reduced numbers of cutaneous T regulatory (Treg) cells and a normal skin barrier. Dock8-/- and mice with an inducible Dock8 deletion in Treg cells exhibited increased allergic skin inflammation after epicutaneous sensitization with OVA. DOCK8 was shown to be important for Treg cell stability at sites of allergic inflammation and for the generation, survival, and suppressive activity of inducible Treg cells. Adoptive transfer of wild-type, but not DOCK8-deficient, OVA-specific, inducible Treg cells suppressed allergic inflammation in OVA-sensitized skin of Dock8-/- mice. These mice developed severe allergic skin inflammation and elevated serum IgE levels after topical exposure to Saureus. Both were attenuated after adoptive transfer of WT but not DOCK8-deficient Treg cells. CONCLUSION: Treg cell dysfunction increases susceptibility to allergic skin inflammation in DOCK8 deficiency and synergizes with cutaneous exposure to Saureus to drive eczema in DOCK8 deficiency.

A Focused Review of Ras Guanine Nucleotide-Releasing Protein 1 in Immune Cells and Cancer.

Four Ras guanine nucleotide-releasing proteins (RasGRP1 through 4) belong to the family of guanine nucleotide exchange factors (GEFs). RasGRPs catalyze the release of GDP from small GTPases Ras and Rap and facilitate their transition from an inactive GDP-bound to an active GTP-bound state. Thus, they regulate critical cellular responses via many downstream GTPase effectors. Similar to other RasGRPs, the catalytic module of RasGRP1 is composed of the Ras exchange motif (REM) and Cdc25 domain, and the EF hands and C1 domain contribute to its cellular localization and regulation. RasGRP1 can be activated by a diacylglycerol (DAG)-mediated membrane recruitment and protein kinase C (PKC)-mediated phosphorylation. RasGRP1 acts downstream of the T cell receptor (TCR), B cell receptors (BCR), and pre-TCR, and plays an important role in the thymocyte maturation and function of peripheral T cells, B cells, NK cells, mast cells, and neutrophils. The dysregulation of RasGRP1 is known to contribute to numerous disorders that range from autoimmune and inflammatory diseases and schizophrenia to neoplasia. Given its position at the crossroad of cell development, inflammation, and cancer, RASGRP1 has garnered interest from numerous disciplines. In this review, we outline the structure, function, and regulation of RasGRP1 and focus on the existing knowledge of the role of RasGRP1 in leukemia and other cancers.

Functional dissection of inherited non-coding variation influencing multiple myeloma risk.

Thousands of non-coding variants have been associated with increased risk of human diseases, yet the causal variants and their mechanisms-of-action remain obscure. In an integrative study combining massively parallel reporter assays (MPRA), expression analyses (eQTL, meQTL, PCHiC) and chromatin accessibility analyses in primary cells (caQTL), we investigate 1,039 variants associated with multiple myeloma (MM). We demonstrate that MM susceptibility is mediated by gene-regulatory changes in plasma cells and B-cells, and identify putative causal variants at six risk loci (SMARCD3, WAC, ELL2, CDCA7L, CEP120, and PREX1). Notably, three of these variants co-localize with significant plasma cell caQTLs, signaling the presence of causal activity at these precise genomic positions in an endogenous chromosomal context in vivo. Our results provide a systematic functional dissection of risk loci for a hematologic malignancy.

IL-21 Rescues the Defect of IL-10-Producing Regulatory B Cells and Improves Allergic Asthma in DOCK8 Deficient Mice.

Mutations in human DOCK8 cause a combined immunodeficiency syndrome characterized by allergic diseases such as asthma and food allergy. However, the underlying mechanism is unclear. Regulatory B (Breg) cells that produce IL-10 exert potent immunosuppressive functions in patients with allergic and autoimmune disorders. DOCK8-deficient B cells show diminished responses to TLR9 signaling, suggesting a possible defect in IL-10-producing Breg cells in those with DOCK8 deficiency, which may contribute to allergies. Here, we isolated peripheral blood mononuclear cells from DOCK8-deficient patients and generated a Dock8 KO mouse model to study the effect of DOCK8 deficiency on Breg cells. DOCK8-deficient patients and Dock8 KO mice harbored quantitative and qualitative defects in IL-10-producing Breg cells; these defects were caused by abnormal Dock8-/- CD4+ T cells. We found that recombinant murine (rm)IL-21 restored the function of Bregs both in vitro and in Dock8 KO mice, leading to reduced inflammatory cell infiltration of the lungs in a murine asthma model. Overall, the results provide new insight into the potential design of Breg-based or IL-21-based therapeutic strategies for allergic diseases, including asthma associated with DOCK8 deficiency.

Cutting Edge: DOCK8 Regulates a Subset of Dendritic Cells That Is Critical for the Development of Experimental Autoimmune Encephalomyelitis.

Dedicator of cytokinesis 8 (DOCK8) is a guanine nucleotide exchange factor with an essential role in cytoskeletal rearrangement, cell migration, and survival of various immune cells. Interestingly, DOCK8-deficient mice are resistant to the development of experimental autoimmune encephalomyelitis (EAE). To understand if EAE resistance in these mice results from an alteration in dendritic cell (DC) functions, we generated mice with conditional deletion of DOCK8 in DCs and observed attenuated EAE in these mice compared with control mice. Additionally, we demonstrated that DOCK8 is important for the existence of splenic conventional DC2 and lymph node migratory DCs and further established that migratory DC, rather than resident DC, are essential for the generation and proliferation of pathogenic T cell populations upon immunization with myelin Ag in adjuvant. Therefore, our data suggest that limiting migratory DCs through DOCK8 deletion and possibly other mechanisms could limit the development of CNS autoimmunity.

Altered function and differentiation of age-associated B cells contribute to the female bias in lupus mice.

Differences in immune responses to viruses and autoimmune diseases such as systemic lupus erythematosus (SLE) can show sexual dimorphism. Age-associated B cells (ABC) are a population of CD11c+T-bet+ B cells critical for antiviral responses and autoimmune disorders. Absence of DEF6 and SWAP-70, two homologous guanine exchange factors, in double-knock-out (DKO) mice leads to a lupus-like syndrome in females marked by accumulation of ABCs. Here we demonstrate that DKO ABCs show sex-specific differences in cell number, upregulation of an ISG signature, and further differentiation. DKO ABCs undergo oligoclonal expansion and differentiate into both CD11c+ and CD11c- effector B cell populations with pathogenic and pro-inflammatory function as demonstrated by BCR sequencing and fate-mapping experiments. Tlr7 duplication in DKO males overrides the sex-bias and further augments the dissemination and pathogenicity of ABCs, resulting in severe pulmonary inflammation and early mortality. Thus, sexual dimorphism shapes the expansion, function and differentiation of ABCs that accompanies TLR7-driven immunopathogenesis.

ARHGEF26 enhances Salmonella invasion and inflammation in cells and mice.

Salmonella hijack host machinery in order to invade cells and establish infection. While considerable work has described the role of host proteins in invasion, much less is known regarding how natural variation in these invasion-associated host proteins affects Salmonella pathogenesis. Here we leveraged a candidate cellular GWAS screen to identify natural genetic variation in the ARHGEF26 (Rho Guanine Nucleotide Exchange Factor 26) gene that renders lymphoblastoid cells susceptible to Salmonella Typhi and Typhimurium invasion. Experimental follow-up redefined ARHGEF26's role in Salmonella epithelial cell infection. Specifically, we identified complex serovar-by-host interactions whereby ARHGEF26 stimulation of S. Typhi and S. Typhimurium invasion into host cells varied in magnitude and effector-dependence based on host cell type. While ARHGEF26 regulated SopB- and SopE-mediated S. Typhi (but not S. Typhimurium) infection of HeLa cells, the largest effect of ARHGEF26 was observed with S. Typhimurium in polarized MDCK cells through a SopB- and SopE2-independent mechanism. In both cell types, knockdown of the ARHGEF26-associated protein DLG1 resulted in a similar phenotype and serovar specificity. Importantly, we show that ARHGEF26 plays a critical role in S. Typhimurium pathogenesis by contributing to bacterial burden in the enteric fever murine model, as well as inflammation in the colitis infection model. In the enteric fever model, SopB and SopE2 are required for the effects of Arhgef26 deletion on bacterial burden, and the impact of sopB and sopE2 deletion in turn required ARHGEF26. In contrast, SopB and SopE2 were not required for the impacts of Arhgef26 deletion on colitis. A role for ARHGEF26 on inflammation was also seen in cells, as knockdown reduced IL-8 production in HeLa cells. Together, these data reveal pleiotropic roles for ARHGEF26 during infection and highlight that many of the interactions that occur during infection that are thought to be well understood likely have underappreciated complexity.

[Expression of RASGRP2 in Lung Adenocarcinoma and Its Effect 
on Immune Microenvironment].

BACKGROUND: Lung cancer still has the highest incidence rate and mortality rate nowadays. In recent years, with the emergence of new drugs and the optimization of treatment mode, especially the clinical application of immunotherapy, the prognosis of lung cancer patients has been improved. However, the benefits of immunotherapy are still limited. Therefore, it is necessary to find new biomarkers to predict the prognosis of lung adenocarcinoma patients and explore its impact on the immune microenvironment. METHODS: The Cancer Genome Atlas (TCGA) database was used to analyze the gene sequencing and clinical data of patients with lung adenocarcinoma. The distribution of RASGRP2 in lung adenocarcinoma was determined by using the human protein mapping database. The Kaplan-Meier plotter database was used to explore the relationship between the expression of RASGRP2 and the prognosis of patients with lung adenocarcinoma. KEGG and GO gene enrichment analysis was performed in patients with high and low expression of RASGRP2. TCGA database was used to analyze the co-expression genes of RASGRP2 and TIMER database was used to calculate the immune related lymphoid infiltration of RASGRP2 and its coexpression genes. The relationship between RASGRP2 expression and immune checkpoint expression was analyzed by using TIMER 2.0 database. RESULTS: We found that RASGRP2 was low expressed in lung adenocarcinoma, and its expression level was related to the prognosis of patients. The high expression of RASGRP2 was involved in the process of hematopoietic cell formation and cell adhesion, and RASGRP2 played an important role in the process of T cell activation. Through TCGA database analysis, ZAP70, TBC1D10C, RASAL3, FGD2, CD37 and ACAP1 were significantly correlated with RASGRP2. The high expression of these genes leaded to the increase of the proportion of CD8+ T cells, memory CD4+ T cells, and the decrease of the proportion of neutrophils and Treg cells. Finally, we found that the expression of RASGRP2 was significantly correlated with the expression of CD274, CTLA4, LAG3 and TIGIT. CONCLUSIONS: RASGRP2 was abnormally expressed in lung adenocarcinoma and correlated with the infiltration level of immune related cells, which might influence the efficacy of immunotherapy.

DOCK8 deficiency causes a skewing to type 2 immunity in the gut with expansion of group 2 innate lymphoid cells.

Dedicator of cytokinesis 8 (DOCK8) is a guanine nucleotide exchange factor (GEF) for Cdc42. In humans, homozygous or compound heterozygous deletions in DOCK8 cause a combined immunodeficiency characterized by various allergic diseases including food allergies. Although group 2 innate lymphoid cells (ILC2s) contribute to the development of allergic inflammation by producing interleukin (IL)-5 and IL-13, the role of ILC2s in DOCK8 deficiency has not been fully explored. With the use of cytometry by time-of-flight (CyTOF), we performed high-dimensional phenotyping of intestinal immune cells and found that DOCK8-deficient (Dock8-/-) mice exhibited expansion of ILC2s and other leukocytes associated with type 2 immunity in the small intestine. Moreover, IL-5- and IL-13-producing cells markedly increased in Dock8-/- mice, and the majority of them were lineage-negative cells, most likely ILC2s. Intestinal ILC2s expanded when DOCK8 expression was selectively deleted in hematopoietic cells. Importantly, intestinal ILC2 expansion was also observed in Dock8VAGR mice having mutations in the catalytic center of DOCK8, thereby failing to activate Cdc42. Our findings indicate that DOCK8 is a negative regulator of intestinal ILC2s to inhibit their expansion via Cdc42 activation, and that deletion of DOCK8 causes a skewing to type 2 immunity in the gut.

Hemolysis inhibits humoral B-cell responses and modulates alloimmunization risk in patients with sickle cell disease.

Red blood cell alloimmunization remains a barrier for safe and effective transfusions in sickle cell disease (SCD), but the associated risk factors remain largely unknown. Intravascular hemolysis, a hallmark of SCD, results in the release of heme with potent immunomodulatory activity, although its effect on SCD humoral response, specifically alloimmunization, remains unclear. Here, we found that cell-free heme suppresses human B-cell plasmablast and plasma cell differentiation by inhibiting the DOCK8/STAT3 signaling pathway, which is critical for B-cell activation, as well as by upregulating heme oxygenase 1 (HO-1) through its enzymatic byproducts, carbon monoxide and biliverdin. Whereas nonalloimmunized SCD B cells were inhibited by exogenous heme, B cells from the alloimmunized group were nonresponsive to heme inhibition and readily differentiated into plasma cells. Consistent with a differential B-cell response to hemolysis, we found elevated B-cell basal levels of DOCK8 and higher HO-1-mediated inhibition of activated B cells in nonalloimmunized compared with alloimmunized SCD patients. To overcome the alloimmunized B-cell heme insensitivity, we screened several heme-binding molecules and identified quinine as a potent inhibitor of B-cell activity, reversing the resistance to heme suppression in alloimmunized patients. B-cell inhibition by quinine occurred only in the presence of heme and through HO-1 induction. Altogether, these data suggest that hemolysis can dampen the humoral B-cell response and that B-cell heme responsiveness maybe a determinant of alloimmunization risk in SCD. By restoring B-cell heme sensitivity, quinine may have therapeutic potential to prevent and inhibit alloimmunization in SCD patients.

Applications of Mouse Models to the Study of Food Allergy.

Mouse models of allergic disease offer numerous advantages when compared to the models of other animals. However, selection of appropriate mouse models is critical to advance the field of food allergy by revealing mechanisms of allergy and for testing novel therapeutic approaches. All current mouse models for food allergy have weaknesses that may limit their applicability to human disease. Aspects such as the genetic predisposition to allergy or tolerance from the strain of mouse used, allergen dose, route of exposure (oral, intranasal, intraperitoneal, or epicutaneous), damage of the epithelial barrier, use of adjuvants, food matrix effects, or composition of the microbiota should be considered prior to the selection of a specific murine model and contemplated according to the intended purpose of the study. This chapter reviews our current knowledge on the application of mouse models to food allergy research and the variables that may influence the successful development of each type of model.

Dysregulated RASGRP1 expression through RUNX1 mediated transcription promotes autoimmunity.

RasGRP1 is a Ras guanine nucleotide exchange factor, and an essential regulator of lymphocyte receptor signaling. In mice, Rasgrp1 deletion results in defective T lymphocyte development. RASGRP1-deficient patients suffer from immune deficiency, and the RASGRP1 gene has been linked to autoimmunity. However, how RasGRP1 levels are regulated, and if RasGRP1 dosage alterations contribute to autoimmunity remains unknown. We demonstrate that diminished Rasgrp1 expression caused defective T lymphocyte selection in C57BL/6 mice, and that the severity of inflammatory disease inversely correlates with Rasgrp1 expression levels. In patients with autoimmunity, active inflammation correlated with decreased RASGRP1 levels in CD4+ T cells. By analyzing H3K27 acetylation profiles in human T cells, we identified a RASGRP1 enhancer that harbors autoimmunity-associated SNPs. CRISPR-Cas9 disruption of this enhancer caused lower RasGRP1 expression, and decreased binding of RUNX1 and CBFB transcription factors. Analyzing patients with autoimmunity, we detected reduced RUNX1 expression in CD4+ T cells. Lastly, we mechanistically link RUNX1 to transcriptional regulation of RASGRP1 to reveal a key circuit regulating RasGRP1 expression, which is vital to prevent inflammatory disease.

KALRN mutations promote antitumor immunity and immunotherapy response in cancer.

BACKGROUND: kalirin RhoGEF kinase (KALRN) is mutated in a wide range of cancers. Nevertheless, the association between KALRN mutations and the pathogenesis of cancer remains unexplored. Identification of biomarkers for cancer immunotherapy response is crucial because immunotherapies only show beneficial effects in a subset of patients with cancer. METHODS: We explored the correlation between KALRN mutations and antitumor immunity in 10 cancer cohorts from The Cancer Genome Atlas program by the bioinformatics approach. Moreover, we verified the findings from the bioinformatics analysis with in vitro and in vivo experiments. We explored the correlation between KALRN mutations and immunotherapy response in five cancer cohorts receiving immune checkpoint blockade therapy. RESULTS: Antitumor immune signatures were more enriched in KALRN-mutated than KALRN-wildtype cancers. Moreover, KALRN mutations displayed significant correlations with increased tumor mutation burden and the microsatellite instability or DNA damage repair deficiency genomic properties, which may explain the high antitumor immunity in KALRN-mutated cancers. Also, programmed cell death 1 ligand (PD-L1) expression was markedly upregulated in KALRN-mutated versus KALRN-wildtype cancers. The increased antitumor immune signatures and PD-L1 expression in KALRN-mutated cancers may favor the response to immune checkpoint blockade therapy in this cancer subtype, as evidenced in five cancer cohorts receiving antiprogrammed cell death protein 1 (PD-1)/PD-L1/cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) immunotherapy. Furthermore, the significant association between KALRN mutations and increased antitumor immunity was associated with the fact that KALRN mutations compromised the function of KALRN in targeting Rho GTPases for the regulation of DNA damage repair pathways. In vitro and in vivo experiments validated the association of KALRN deficiency with antitumor immunity and the response to immune checkpoint inhibitors. CONCLUSIONS: The KALRN mutation is a useful biomarker for predicting the response to immunotherapy in patients with cancer.

DOCK2 couples with LEF-1 to regulate B cell metabolism and memory response.

Dedicator of cytokinesis 2 (DOCK2) is essential for the B cell differentiation, BCR signaling and humoral immune response. However, the role of DOCK2 in the memory response of B cell is unknown. By using two DOCK2 deficient patients, we found that the memory B cells were decreased and the early activation of DOCK2 deficient memory B cells was abolished to the degree of naïve B cells due to the decreased expression of CD19 and CD21 mechanistically. Interestingly the expression of LEF-1, a negative regulator of CD21, was increased in DOCK2 deficient B cells. This was linked to the increased expression of HIF-1α and cell metabolism, which in turn affected the ER structure. Finally, the reduction of memory B cells in DOCK2 patients was due to the increased apoptosis, which might be related with the increased metabolism.

SON DNA-binding protein mediates macrophage autophagy and responses to intracellular infection.

Intracellular pathogens affect diverse host cellular defence and metabolic pathways. Here, we used infection with Francisella tularensis to identify SON DNA-binding protein as a central determinant of macrophage activities. RNAi knockdown of SON increases survival of human macrophages following F. tularensis infection or inflammasome stimulation. SON is required for macrophage autophagy, interferon response factor 3 expression, type I interferon response and inflammasome-associated readouts. SON knockdown has gene- and stimulus-specific effects on inflammatory gene expression. SON is required for accurate splicing and expression of GBF1, a key mediator of cis-Golgi structure and function. Chemical GBF1 inhibition has similar effects to SON knockdown, suggesting that SON controls macrophage functions at least in part by controlling Golgi-associated processes.

MHC-restricted phosphopeptide antigens: preclinical validation and first-in-humans clinical trial in participants with high-risk melanoma.

BACKGROUND: Phosphorylated peptides presented by MHC molecules represent a new class of neoantigens expressed on cancer cells and recognized by CD8 T-cells. These peptides are promising targets for cancer immunotherapy. Previous work identified an HLA-A*0201-restricted phosphopeptide from insulin receptor substrate 2 (pIRS2) as one such target. The purpose of this study was to characterize a second phosphopeptide, from breast cancer antiestrogen resistance 3 (BCAR3), and to evaluate safety and immunogenicity of a novel immunotherapic vaccine comprising either or both of these phosphorylated peptides. METHODS: Phosphorylated BCAR3 protein was evaluated in melanoma and breast cancer cell lines by Western blot, and recognition by T-cells specific for HLA-A*0201-restricted phosphorylated BCAR3 peptide (pBCAR3126-134) was determined by 51Cr release assay and intracellular cytokine staining. Human tumor explants were also evaluated by mass spectrometry for presentation of pIRS2 and pBCAR3 peptides. For the clinical trial, participants with resected stage IIA-IV melanoma were vaccinated 6 times over 12 weeks with one or both peptides in incomplete Freund's adjuvant and Hiltonol (poly-ICLC). Adverse events (AEs) were coded based on National Cancer Institute (NCI) Common Terminology Criteria for Adverse Events (CTCAE) V.4.03, with provision for early study termination if dose-limiting toxicity (DLT) rates exceeded 33%. The enrollment target was 12 participants evaluable for immune response to each peptide. T-cell responses were assessed by interferon-γ ELISpot assay. RESULTS: pBCAR3 peptides were immunogenic in vivo in mice, and in vitro in normal human donors, and T-cells specific for pBCAR3126-134 controlled outgrowth of a tumor xenograft. The pIRS21097-1105 peptide was identified by mass spectrometry from human hepatocellular carcinoma tumors. In the clinical trial, 15 participants were enrolled. All had grade 1 or 2 treatment-related AEs, but there were no grade 3-4 AEs, DLTs or deaths on study. T-cell responses were induced to the pIRS21097-1105 peptide in 5/12 patients (42%, 90% CI 18% to 68%) and to the pBCAR3126-134 peptide in 2/12 patients (17%, 90% CI 3% to 44%). CONCLUSION: This study supports the safety and immunogenicity of vaccines containing the cancer-associated phosphopeptides pBCAR3126-134 and pIRS21097-1105, and the data support continued development of immune therapy targeting phosphopeptides. Future studies will define ways to further enhance the magnitude and durability of phosphopeptide-specific immune responses. TRIAL REGISTRATION NUMBER: NCT01846143.

[Immunosenescence: The Forefront of Infection and Trophic Control].

Recently, aging is becoming an important social problem in many developed countries including Japan. It is socially and universally important to unveil the impact of aging and extend healthy life expectancy. Here we show our recent finding that dedicator of cytokinesis 11 (DOCK11, also known as Zizimin2) may be involved in immunosenescence of B cells. DOCK11 was identified as a guanine nucleotide exchange factor for a small GTPase called cell division cycle 42. Expression of DOCK11 is restricted to lymphoid tissues, and becomes downregulated with age. Thus we examined the involvement of DOCK11 in immunosenescence of B-1a B cells as an example. B-1a cells are the main source of antibodies at steady state, and function as the first line of defense against infection. Although DOCK11 was expressed by B-1a cells, the expression levels declined with age. Furthermore, production of anti-pneumococcal immunoglobulin M antibodies was suppressed in aged mice, and was recovered by adoptive transfer with B-1a cells in a DOCK11-dependent manner. Thus DOCK11 may be involved in immunosenescence of B-1a cells.

Expression of DOCK10.1 protein revealed with a specific antiserum: insights into regulation of first exon isoforms of DOCK10.

DOCK10, a guanine-nucleotide exchange factor (GEF) for Rho GTPases, represents the example of a gene that gives rise to alternative first exon mRNA isoforms, named DOCK10.1 and DOCK10.2. Expression of human DOCK10.2 protein in cell lines, and its induction by interleukin-4 (IL-4) in normal B lymphocytes and chronic lymphocytic leukemia (CLL) cells, were previously demonstrated using an antiserum raised against a peptide encoded by sequences from exon 1.2. Here, expression of human DOCK10.1 protein was demonstrated using an antiserum raised against a peptide encoded by sequences from exon 1.1. Specificity of the DOCK10.1 and DOCK10.2 antisera for their respective isoforms was demonstrated using transfected human 293 T cells. Their specificity for endogenous DOCK10 was strongly suggested by the high significance of the correlations between the levels of their expected signals at the molecular size of 250 kDa and the levels of DOCK10.1 and DOCK10.2 mRNAs, respectively, in human hematopoietic cell lines. Specificity of the DOCK10.1 antiserum for DOCK10 was also demostrated in mouse using the DOCK10 knockout model. The DOCK10.1 protein was induced by IL-4 in CLL cells, which demonstrates that the mechanism by which IL-4 regulates DOCK10 is not isoform-specific. Last, to get insights into differential regulation of the DOCK10 isoforms, their protein levels in cell lines were compared with their gene expression profiles retrieved from the Cancer Cell Line Encyclopedia (CCLE), leading to the identification of BCL3 and KLF12 as potential transcriptional regulators of DOCK10.1 and DOCK10.2, respectively.