Complete analysis of the B-cell response to a protein antigen, from in vivo germinal centre formation to 3-D modelling of affinity maturation

Somatic hypermutation of immunoglobulin variable region genes occurs within germinal centres (GCs) and is the process responsible for affinity maturation of antibodies during an immune response. Previous studies have focused almost exclusively on the immune response to haptens, which may be unrepresentative of epitopes on protein antigens. In this study, we have exploited a model system that uses transgenic B and CD4<sup>+</sup> T cells specific for hen egg lysozyme (HEL) and a chicken ovalbumin peptide, respectively, to investigate a tightly synchronized immune response to protein antigens of widely differing affinities, thus allowing us to track many facets of the development of an antibody response at the antigen-specific B cell level in an integrated system <i>in</i> <i>vivo</i>. Somatic hypermutation of immunoglobulin variable genes was analysed in clones of transgenic B cells proliferating in individual GCs in response to HEL or the cross-reactive low-affinity antigen, duck egg lysozyme (DEL). Molecular modelling of the antibody–antigen interface demonstrates that recurring mutations in the antigen-binding site, selected in GCs, enhance interactions of the antibody with DEL. The effects of these mutations on affinity maturation are demonstrated by a shift of transgenic serum antibodies towards higher affinity for DEL in DEL-cOVA immunized mice. The results show that B cells with high affinity antigen receptors can revise their specificity by somatic hypermutation and antigen selection in response to a low-affinity, cross-reactive antigen. These observations shed further light on the nature of the immune response to pathogens and autoimmunity and demonstrate the utility of this novel model for studies of the mechanisms of somatic hypermutation

Treatment adherence among sputum smear-positive pulmonary tuberculosis patients in mountainous areas in China

<p>Abstract</p> <p>Background</p> <p>We carried out an investigation in five provinces in China to assess treatment adherence and identify factors associated with insufficient treatment adherence in tuberculosis (TB) patients in mountainous, rural areas of China.</p> <p>Methods</p> <p>In each of the five provinces, all counties with > 80% mountainous area were stratified into three groups according to their gross domestic product. In each stratum, one county was randomly sampled. Study subjects were sampled from all smear positive TB cases registered in 2007 in the target counties. TB patients, village doctors, county doctors and directors of the TB prevention and control institutes were interviewed. Insufficient medication adherence was defined as taking less than 90% of anti-TB drug doses prescribed. Insufficient re-examination adherence was defined as having less than the recommended three sputum smear examinations during the treatment course.</p> <p>Results</p> <p>A minority of patients took drugs under direct observation: on average 29% during the intensive phase of treatment. In total, 524 TB patients were included, of whom 49 (9.4%) took less than 90% of all doses prescribed and 92 (17.6%) did not have all sputum smear examinations, with substantial variations between the provinces. In multivariable analysis, no direct observation of treatment during the intensive phase and the presence of adverse events were associated both with insufficient medication adherence and insufficient re-examination adherence. Overall, 79% of patients were adherent both to treatment and re-examinations.</p> <p>Conclusions</p> <p>In these remote and poor areas of China, the TB control program is not fully functioning according to the guidelines. The majority of patients are not treated under direct observation, while direct observation by health care staff was associated with better adherence, both to drug therapy and re-examinations. Insufficient adherence increases the risk of unsuccessful treatment outcomes and development of drug resistance. Measures should be taken urgently in these areas to strengthen implementation of the international Stop TB strategy.</p

Stroke and Mortality Risk in Patients With Various Patterns of Atrial Fibrillation Results From the ENGAGE AF-TIMI 48 Trial (Effective Anticoagulation With Factor Xa Next Generation in Atrial Fibrillation-Thrombolysis in Myocardial Infarction 48)

Background-Whether the pattern of atrial fibrillation (AF) modifies the risk/benefit of anticoagulation is controversial. In ENGAGE AF-TIMI 48 trial (Effective Anticoagulation with Factor Xa Next Generation in Atrial Fibrillation-Thrombolysis in Myocardial Infarction 48), the factor Xa inhibitor edoxaban was noninferior to warfarin in preventing stroke or systemic embolic events and significantly reduced bleeding and cardiovascular mortality. However, detailed analyses by AF pattern have not been reported.Methods and Results-The 21 105 patients were categorized as having paroxysmal (= 7 days but = 1 year or failed cardioversion) AF patterns at randomization. Efficacy and safety outcomes were evaluated during the 2.8 years median follow-up and compared by AF pattern. The primary end point of stroke/systemic embolic event was lower in those patients with paroxysmal AF (1.49%/year), compared with persistent (1.83%/year; P-adj =0.015) and permanent AF (1.95%/year; P-adj =0.004). Overall, all-cause mortality also was lower with paroxysmal (3.0%/year) compared with persistent (4.4%/year; P-adj <0.001) and permanent AF (4.4%/year; P-adj <0.001). Annualized major bleeding rates were similar across AF patterns (2.86% versus 2.65% versus 2.73%). There was no effect modification by treatment assignment.Conclusions-In ENGAGE AF-TIMI 48 trial, patients with paroxysmal AF suffered fewer thromboembolic events and deaths compared with those with persistent and permanent AF. The efficacy and safety profile of edoxaban as compared with warfarin was consistent across the 3 patterns of AF.Daiichi-Sankyo Pharma In