Cdc42 is a key regulator of B cell differentiation and is required for antiviral humoral immunity

The small Rho GTPase Cdc42, known to interact with Wiskott–Aldrich syndrome (WAS) protein, is an important regulator of actin remodeling. Here, we show that genetic ablation of Cdc42 exclusively in the B cell lineage is sufficient to render mice unable to mount antibody responses. Indeed Cdc42-deficient mice are incapable of forming germinal centers or generating plasma B cells upon either viral infection or immunization. Such severe immune deficiency is caused by multiple and profound B cell abnormalities, including early blocks during B cell development; impaired antigen-driven BCR signaling and actin remodeling; defective antigen presentation and in vivo interaction with T cells; and a severe B cell–intrinsic block in plasma cell differentiation. Thus, our study presents a new perspective on Cdc42 as key regulator of B cell physiology.B cells provide a critical line of defense from pathogenic infections through the production of highly specific antibodies. The initial stages of B cell development occur in the bone marrow, where hematopoietic stem cells undergo stepwise rearrangements of the genes encoding the B cell receptor (BCR) and changes in the expression of cell surface receptors (Hardy et al., 1991). Immature B cells egress the bone marrow and migrate to the spleen to complete their development, going through transitional stages. Mature follicular B cells then recirculate throughout the body in search for cognate antigen, continually entering secondary lymphoid organs, including the LNs and spleen. Specific recognition of antigen by the BCR provides the first signal required for B cell activation. Typically, a second signal is required for maximal activation and is provided by CD4⁺ helper T cells after the presentation of processed antigen on the B cell surface. These two signals in combination trigger the proliferation and differentiation of B cells, which go on to form antibody-secreting plasma cells and to establish germinal center responses for affinity maturation (Rajewsky, 1996).B cell activation in vivo is predominantly triggered by antigen on the surface of a presenting cell (Batista and Harwood, 2009). The prevalence of this mode of activation has brought about a reevaluation of the importance of the cytoskeleton, given that the recognition of tethered antigen requires considerable alteration in B cell morphology (Fleire et al., 2006). Antigen-induced BCR signaling leads to radical reorganization of the actin cytoskeleton resulting in the modification of the BCR dynamics at the cell surface (Hao and August, 2005; Treanor et al., 2010; Treanor et al., 2011). Moreover the binding of membrane-bound antigen to cognate BCR triggers a cascade of intracellular signaling events that induces actin-dependent spreading of the B cell across the antigen-containing surface (Weber et al., 2008; Sohn et al., 2008; Depoil et al., 2008). However the mediators that link BCR signaling with reorganization of the actin cytoskeleton are currently not well defined.Among actin regulators, the RhoGTPases are a highly conserved family that function as molecular switches by cycling between inactive GDP (guanosine diphosphate) and active GTP (guanosine triphosphate) bound states (Tybulewicz and Henderson, 2009). RhoGTPase activity is modulated by G-nucleotide exchange factors (GEF) that promote the formation of the GTP-bound state and binding to various effectors involved in actin reorganization. Conversely, GTPase-activating proteins (GAP) catalyze the hydrolysis of GTP and thereby switch off RhoGTPase activity. The importance of the RhoGTPases as a whole in the regulation of B cell responses is highlighted by the far-reaching consequences that impaired activity of several GEFs, such as Vav and DOCK8, has on humoral immune responses (Doody et al., 2001; Fujikawa et al., 2003; Randall et al., 2009; Zhang et al., 2009).The importance of Rho GTPases in B cell physiology has been well established. For example, RhoA has been shown to regulate BCR signaling by influencing inositol-3 phosphate synthesis and calcium signaling (Saci and Carpenter, 2005). Moreover, B cell–specific inactivation of both Rac1 and Rac2 leads to virtually complete absence of B cells (Walmsley et al., 2003), and inactivation of Rac1 results in defects in spreading in transitional cells (Brezski and Monroe, 2007). However, although the inactivation of Rac2 leads to defects in B cell adhesion and synapse formation, it is unclear whether these proteins are involved in actin-dependent spreading in mature B cells (Arana et al., 2008).Cdc42 has been little characterized in B cells, in spite of its proven chief role as an essential regulator of cell cycle (Johnson and Pringle, 1990), cell polarity (Etienne-Manneville, 2004), and actin cytoskeleton in other cellular systems. This is likely due, at least in part, to the reported mild phenotype of mice lacking Cdc42 in B cells (Guo et al., 2009) compared with the severe deficiencies observed in animals lacking Rac family members (Walmsley et al., 2003). However, the mild phenotype is somehow surprising given that Cdc42 directly or indirectly associates with Wiskott–Aldrich Syndrome Protein (WASp) and in complex with Arp2/3 regulates cytoskeleton remodeling (Symons et al., 1996; Aspenström et al., 1996; Kolluri et al., 1996). Importantly, mutations in WAS gene lead to a X-linked, recessive disease characterized by recurrent infections, abnormal lymphocyte function, as well as an increased risk for systemic autoimmunity (Derry et al., 1994; Sullivan et al., 1994). WASp deficient B cells play a primary role in driving autoimmunity (Becker-Herman et al., 2011). The Cdc42 effectors WASp and N-WASp have both been implicated the regulation of actin reorganization in response to BCR antigen engagement (Westerberg et al., 2012; Liu et al., 2013). Besides, expression of a dominant negative form of Cdc42 in B cells leads to alterations of the actin cytoskeleton (Westerberg et al., 2001). In addition, Cdc42 has been shown to play a role in the polarization and secretion of lysosomal protein involved in antigen extraction (Yuseff et al., 2011).Here, we used a strategy harnessing the mb1 promoter to generate mice with a selective and very effective deletion of Cdc42 in early B cell progenitors (Hobeika et al., 2006). Using this model, we demonstrated that Cdc42 plays an essential role in many aspects of B cell biology, including the formation of mature B cells and the establishment of antibody responses. We went on to dissect the underlying cause of the severe immunodeficiency of these mice and found that Cdc42-deficient B cells exhibit defects in BCR signaling and presentation of internalized antigen, leading to reduced B–T cell interactions and the absence of germinal center responses in vivo. Moreover, Cdc42-deficient B cells can normally proliferate and class switch when stimulated with CD40 or LPS, but they are completely impaired in their ability to differentiate into plasma cells. Together, these attributes render Cdc42-deficient mice unable to mount antibody responses after immunization with model antigen or viral infection, and highlight a fundamental role for this RhoGTPase in the regulation of B cell responses.     

What should men living with haemophilia need to know? The perspectives of Canadian men with haemophilia

Haemophilia is an inherited bleeding disorder affecting approximately 3000 Canadian men (Walker 2012). To manage their disease effectively individuals must be knowledgeable about the disease, bleed prevention strategies, treatment approaches, and complications. Data on individuals’ knowledge levels are scarce. The availability of such data could lead to better educational strategies for disease management. The aim of this study was to determine current knowledge levels, needs and gaps among Canadian individuals with haemophilia to facilitate optimal disease management. A survey was disseminated to adult males with haemophilia at three Haemophilia Treatment Centres (HTCs) in Canada. Self‐reported current knowledge levels and knowledge seeking were measured. Survey respondents reported highest levels of knowledge in the following areas: identifying and treating a bleed, haemophilia and physical activity, travel, career issues and genetics. Lower levels of knowledge were reported in the areas of sexual activity, product safety, information about factor, haemophilia and ageing, advocacy, timing of prophylactic infusions, and new or alternative therapies. Treating a bleed was the most commonly sought information, followed by information about factor, product safety, identifying a bleed and other health care issues. There was a positive correlation between knowledge seeking and severity of disease. HTC attendance was associated with knowledge seeking, and HTCs were the most frequented knowledge source, followed by the Canadian Haemophilia Society website. Canadian men were well informed; the HTC's role in knowledge sharing was recognized. Timing of infusions, sexual activity and ageing are areas which should be targeted in knowledge sharing.     

Physical activity and health outcomes in persons with haemophilia B

Regular participation in physical activity helps to prevent damage and maintain joint health in persons with haemophilia. This study describes self‐reported physical activity participation among a sample of people with haemophilia B in the US and measures its association with health‐related quality of life (HRQoL). Data on 135 participants aged 5–64 years were abstracted from Hemophilia Utilization Group Study Part Vb. The International Physical Activity Questionnaire assessed physical activity among participants aged 15–64 years, and the Children's Physical Activity Questionnaire abstracted from the Canadian Community Health Survey was used for participants aged 5–14 years. SF‐12 was used to measure HRQoL and the EuroQol (EQ‐5D‐3L) was used to measure health status for participants older than 18 years of age. PedsQL was used to measure HRQoL in children aged 5–18 years. Sixty‐two percent of participants in the 15–64 year‐old age cohort reported a high level of physical activity, 29% reported moderate activity and 9% reported low activity. For children aged 5–14 years, 79% reported participating in physical activity for at least 4 days over a typical week. Based on the 2008 Physical Activity Guidelines for Americans, 79% of adults achieved the recommended physical activity level. Multivariable regression models indicated that adults who engaged in a high level of physical activity reported EQ‐5D Visual Analogue Scale (VAS) scores that were 11.7 (P = 0.0726) points greater than those who engaged in moderate/low activity, indicating better health outcomes. Among children, no statistically significant differences in health outcomes were found between high and moderate or low activity groups.     

Validation of the Chinese version of the Canadian Haemophilia Outcomes‐Kids' Life Assessment Tool (the CHO‐KLAT)

It is important to assess the health‐related quality of life outcomes of boys in China, but there are no tools validated for this purpose. The objective of the study was to assess the validity of the Simplified Chinese version of the CHO‐KLAT_2.0. We recruited 60 boys with either haemophilia A (HA) or haemophilia B (HB) and their parents from four regions in China, and assessed the validity of CHO‐KLAT compared to the PedsQL. All participants complete the CHO‐KLAT a second time 1–2 weeks later to assess reliability. The boys ranged in age from 7 to 18 (mean = 12.4; SD = 3.03) years. The severity distribution was: mild (9), moderate (10) and severe (41). On‐demand therapy was received by 26 boys, while 18 received low‐dose prophylaxis (HA: 10 IU kg^?1 2–3 times week^?1, and HB: 20 IU kg^?1 1 time week^?1). The mean CHO‐KLAT scores were 63.7 (SD = 10.6) for child‐report and 58.3 (SD = 11.4) for parent‐report. Validity was supported by a correlation of 0.67 (P < 0.0001) with the PedsQL for child‐report and 0.64 (P < 0.0001) for parent‐report. The test–retest reliability was 0.88 (95% CI: 0.82–0.94) for child‐report, and 0.90 (95% CI: 0.86–0.95) for parent‐report. Inter‐rater reliability was 0.46 (95% CI: 0.26–0.66). CHO‐KLAT scores were 11 points higher among patients who had been on prophylaxis 3 times per week for ≥24 weeks. These results confirm the reliability and validity of the Chinese version of the CHO‐KLAT. This measure is suitable for use in prospective clinical trials in boys with haemophilia in China.     

‘Train‐the‐Trainer’: an effective and successful model to accelerate training and improve physiotherapy services for persons with haemophilia in China

The objective of this study was to teach a small group of Chinese physiatrists and physiotherapists to: (i) become trainers and leaders in haemophilia physiotherapy (PT) care in China and (ii) to acquire rapid proficiency in using the reliable and validated Hemophilia Joint Health Score (HJHS) for evaluating musculoskeletal health in boys with haemophilia. Two experienced Canadian physiotherapists and co‐developers of the HJHS moderated a 4‐day PT training workshop with six Chinese participants. Emphasis was placed on instruction and practice in administering the HJHS. Practical sessions with haemophilia patients were interchanged with theory (power point presentations) and interactive question and answer periods. A proficient, knowledgeable translator was an essential component of the workshop. Upon workshop completion, the six trainees demonstrated improved haemophilia‐specific PT knowledge and were fully familiar with the HJHS and its administration. The latter was assessed in a mini‐reliability study. The ‘Train‐the‐Trainer’ model is a very effective education programme designed to accelerate training in haemophilia PT to meet the rapidly increasing need for haemophilia‐specific rehabilitation services in a very large country such as China. It is anticipated that physiatrists/physiotherapists at newly established Chinese haemophilia treatment centres will receive training in haemophilia care as a result of this unique programme in the immediate future.     

Daily Physical Activity,Functional Capacity and Quality of Life in Patients with COPD

Introduction: In the therapy of chronic obstructive pulmonary disease (COPD), it is a major goal to improve health-related quality of life (HRQOL). Patients with COPD often suffer from exertional dyspnea and adopt a sedentary lifestyle, which could be associated with poorer HRQOL. The aim of this study was to investigate the independent association of objectively measured daily physical activity and functional capacity with HRQOL in patients with COPD. Methods: In this cross-sectional study conducted at the University Hospital Basel, Switzerland, 87 stable patients (58.6% male, mean age: 67.3 ± 9.6 yrs) with COPD in GOLD grades I (n = 23), II (n = 46), III (n = 12) and IV (n = 6) were investigated. To assess HRQOL, the COPD assessment test (CAT) was completed. Patients performed spirometry and 6-min walk test. Physical activity was measured by the SenseWear Mini Armband on 7 consecutive days. By performing a multiple linear regression analysis, independent predictors of CAT score were identified. Results: Age (β = ?0.39, p = 0.001), average daily steps (β = ?0.31, p = 0.033) and 6-min walk distance (β = ?0.32, p = 0.019) were found to be independent predictors of CAT score, whereas physical activity duration above 3 METs (p = 0.498) and forced expiratory volume in 1 s in% of predicted (p = 0.364) showed no significant association. Conclusions: This study showed that average daily steps and functional capacity are independent determinants of HRQOL in patients with COPD. This emphasizes the importance to remain active and mobile, which is associated with better HRQOL.