Defence Engagement (Health) between the UK and Ireland since the Good Friday Agreement in 1998.

This paper describes the range of Defence Engagement (Health) (DE(H)) activities between Northern Ireland and Ireland following the Good Friday Agreement in April 1998. Although the Agreement made provision for cross-border cooperation in health, the Omagh bombing of August 1998 energised the discussion to provide greater co-ordination of future responses to mass casualty events. The paper describes these DE(H) activities at the Strategic, Operational and Tactical levels to show the integration across these levels and between the agencies of both governments. The paper shows how a DE(H) programme can have a successful strategic effect by finding topics of mutual interest that can bring together two countries in order to provide an effective health and social care provision. This paper forms part of a special issue of BMJ Military Health dedicated to Defence Engagement (.

Practices and perspectives on advanced diagnostic and interventional bronchoscopy among pediatric pulmonologists in the United States.

INTRODUCTION: Advanced diagnostic bronchoscopy includes endobronchial ultrasound (EBUS) guided transbronchial lung and lymph node biopsies, CT navigation and robotic bronchoscopy. Interventional bronchoscopy refers to procedures performed for therapeutic purposes such as balloon dilation of the airway, tissue debulking, cryotherapy, removal of foreign bodies and insertion of endobronchial valves [1]. For adult patients, these procedures are standard of care [2, 3]. Despite a lack of formalized training, there are numerous case reports and case series describing the use of advanced diagnostic and interventional bronchoscopy techniques in children. The safety and feasibility of EBUS-TBNA, cryotherapy techniques, endobronchial valves among other techniques have been demonstrated in these publications [1, 4-9]. METHODS: We sought to better understand the current practices and perspectives on interventional and advanced bronchoscopy among pediatric pulmonologists through surveys sent to pediatric teaching hospitals across the United States. RESULTS: We received 43 responses representing 28 programs from 25 states. The highest bronchoscopy procedure volume occurred in the 0-5 years age group. Among our respondents, 31% self-identified as a pediatric interventional/advanced bronchoscopist. 79% believe that advanced and interventional training is feasible in pediatric pulmonology and 77% believe it should be offered to pediatric pulmonary fellows. DISCUSSION: This is the first study to characterize current practices and perspectives regarding advanced diagnostic and interventional bronchoscopy procedures among pediatric pulmonologists in the United States. Pediatric interventional pulmonology (IP) is in its infancy and its beginnings echo those of the adult IP where only certain centers were performing these procedures.

Audit of Ireland's first manual vacuum aspiration service.

INTRODUCTION: Manual vacuum aspiration (MVA) is a safe and effective alternative option for the management of first-trimester miscarriage, termination of pregnancy, or retained pregnancy tissue. Ireland's first MVA clinic was set up in the Rotunda Hospital in April 2020. OBJECTIVE: To identify the number of women who have undergone MVA since establishing our service, to assess the efficacy and safety of MVA in that service, and to develop local Irish studies that further support the safety of MVA, adding to the international body of evidence. METHODS: With the approval and assistance of the Clinical Audit Committee, we obtained a log of all patients who underwent MVA in the first 18 months of the service. We performed a retrospective electronic chart review using Maternal and Newborn Clinical Management System. We collected the data and preformed a descriptive analysis. RESULTS: In total, 86 women underwent MVA, 85 (98.8%) of which were successfully completed. There were no immediate procedural complications, inter-hospital transfers, or emergency electric vacuum aspiration (EVA) required. We obtained an incomplete evacuation rate of 4.7% (n = 4). CONCLUSION: We have demonstrated that the MVA service in the Rotunda Hospital is a safe, effective management option with advantages for both the patient and the healthcare system. We recommend consideration for provision of funding and resources to enable expansion of this service nationally in order to give women greater autonomy of choice in the management of early pregnancy complications and termination of pregnancy.

Zinc Gluconate Induces Potentially Cancer Chemopreventive Activity in Barrett's Esophagus: A Phase 1 Pilot Study.

BACKGROUND: Chemopreventive effects of zinc for esophageal cancer have been well documented in animal models. This prospective study explores if a similar, potentially chemopreventive action can be seen in Barrett's esophagus (BE) in humans. AIMS: To determine if molecular evidence can be obtained potentially indicating zinc's chemopreventive action in Barrett's metaplasia. METHODS: Patients with a prior BE diagnosis were placed on oral zinc gluconate (14 days of 26.4 mg zinc BID) or a sodium gluconate placebo, prior to their surveillance endoscopy procedure. Biopsies of Barrett's mucosa were then obtained for miRNA and mRNA microarrays, or protein analyses. RESULTS: Zinc-induced mRNA changes were observed for a large number of transcripts. These included downregulation of transcripts encoding proinflammatory proteins (IL32, IL1ß, IL15, IL7R, IL2R, IL15R, IL3R), upregulation of anti-inflammatory mediators (IL1RA), downregulation of transcripts mediating epithelial-to-mesenchymal transition (EMT) (LIF, MYB, LYN, MTA1, SRC, SNAIL1, and TWIST1), and upregulation of transcripts that oppose EMT (BMP7, MTSS1, TRIB3, GRHL1). miRNA arrays showed significant upregulation of seven miRs with tumor suppressor activity (-125b-5P, -132-3P, -548z, -551a, -504, -518, and -34a-5P). Of proteins analyzed by Western blot, increased expression of the pro-apoptotic protein, BAX, and the tight junctional protein, CLAUDIN-7, along with decreased expression of BCL-2 and VEGF-R2 were noteworthy. CONCLUSIONS: When these mRNA, miRNA, and protein molecular data are considered collectively, a cancer chemopreventive action by zinc in Barrett's metaplasia may be possible for this precancerous esophageal tissue. These results and the extensive prior animal model studies argue for a future prospective clinical trial for this safe, easily-administered, and inexpensive micronutrient, that could determine if a chemopreventive action truly exists.

Ivacaftor for cystic fibrosis: An evaluation of real world utilisation and expenditure in the Irish Healthcare Setting.

In Ireland, Ivacaftor is reimbursed, on the High-Tech Drug Scheme, for the treatment of cystic fibrosis in patients age 6 years and older who have the G551D mutation. The aim of this study was to analyse the utilisation and expenditure of Ivacaftor on this scheme in the 12 month period post-reimbursement. All patients who had received Ivacaftor (regardless of General Medical Services Scheme eligibility/ineligibility) were included. A total of 140 individuals (male=74; 53%) received Ivacaftor over the defined 12 month study period (from January 2015 to December 2015 inclusive). The cohort ranged in age from 6 years to 61 years. The mean age was 22 years; a positive skew in age distribution indicated that a greater number of the cohort were in the younger age groups. No statistically significant difference was detected in the mean ages of the male and female subgroups. Drug acquisition expenditure by the Health Services Executive on Ivacaftor over the 12 month study period was €29.81 million.

Microbial acceleration of aerobic pyrite oxidation at circumneutral pH.

Pyrite (FeS2 ) is the most abundant sulfide mineral on Earth and represents a significant reservoir of reduced iron and sulfur both today and in the geologic past. In modern environments, oxidative transformations of pyrite and other metal sulfides play a key role in terrestrial element partitioning with broad impacts to contaminant mobility and the formation of acid mine drainage systems. Although the role of aerobic micro-organisms in pyrite oxidation under acidic-pH conditions is well known, to date there is very little known about the capacity for aerobic micro-organisms to oxidize pyrite at circumneutral pH. Here, we describe two enrichment cultures, obtained from pyrite-bearing subsurface sediments, that were capable of sustained cell growth linked to pyrite oxidation and sulfate generation at neutral pH. The cultures were dominated by two Rhizobiales species (Bradyrhizobium sp. and Mesorhizobium sp.) and a Ralstonia species. Shotgun metagenomic sequencing and genome reconstruction indicated the presence of Fe and S oxidation pathways in these organisms, and the presence of a complete Calvin-Benson-Bassham CO2 fixation system in the Bradyrhizobium sp. Oxidation of pyrite resulted in thin (30-50 nm) coatings of amorphous Fe(III) oxide on the pyrite surface, with no other secondary Fe or S phases detected by electron microscopy or X-ray absorption spectroscopy. Rates of microbial pyrite oxidation were approximately one order of magnitude higher than abiotic rates. These results demonstrate the ability of aerobic microbial activity to accelerate pyrite oxidation and expand the potential contribution of micro-organisms to continental sulfide mineral weathering around the time of the Great Oxidation Event to include neutral-pH environments. In addition, our findings have direct implications for the geochemistry of modern sedimentary environments, including stimulation of the early stages of acid mine drainage formation and mobilization of pyrite-associated metals.

Piperlongumine promotes autophagy via inhibition of Akt/mTOR signalling and mediates cancer cell death.

BACKGROUND: The Akt/mammalian target of rapamycin (mTOR) signalling pathway serves as a critical regulator of cellular growth, proliferation and survival. Akt aberrant activation has been implicated in carcinogenesis and anticancer therapy resistance. Piperlongumine (PL), a natural alkaloid present in the fruit of the Long pepper, is known to exhibit notable anticancer effects. Here we investigate the impact of PL on Akt/mTOR signalling. METHODS: We examined Akt/mTOR signalling in cancer cells of various origins including prostate, kidney and breast after PL treatment. Furthermore, cell viability after concomitant treatment with PL and the autophagy inhibitor, Chloroquine (CQ) was assessed. We then examined the efficacy of in vivo combination treatment using a mouse xenograft tumour model. RESULTS: We demonstrate for the first time that PL effectively inhibits phosphorylation of Akt target proteins in all tested cells. Furthermore, the downregulation of Akt downstream signalling resulted in decrease of mTORC1 activity and autophagy stimulation. Using the autophagy inhibitor, CQ, the level of PL-induced cellular death was significantly increased. Moreover, concomitant treatment with PL and CQ demonstrated notable antitumour effect in a xenograft mouse model. CONCLUSIONS: Our data provide novel therapeutic opportunities to mediate cancer cellular death using PL. As such, PL may afford a novel paradigm for both prevention and treatment of malignancy.

Hypoxia-inducible factor signalling mechanisms in the central nervous system.

In the CNS, neurones are highly sensitive to the availability of oxygen. In conditions where oxygen availability is decreased, neuronal function can be altered, leading to injury and cell death. Hypoxia has been implicated in a number of central nervous system pathologies including stroke, head trauma and neurodegenerative diseases. Cellular responses to oxygen deprivation are complex and result in activation of short- and long-term mechanisms to conserve energy and protect cells. Failure of synaptic transmission can be observed within minutes following this hypoxia. The acute effects of hypoxia on synaptic transmission are primarily mediated by altering ion fluxes across membranes, pre-synaptic effects of adenosine and other actions at glutamatergic receptors. A more long-term feature of the response of neurones to hypoxia is the activation of transcription factors such as hypoxia-inducible factor. The activation of hypoxia-inducible factor is governed by a family of dioxygenases called hypoxia-inducible factor prolyl 4 hydroxylases (PHDs). Under hypoxic conditions, PHD activity is inhibited, thereby allowing hypoxia-inducible factor to accumulate and translocate to the nucleus, where it binds to the hypoxia-responsive element sequences of target gene promoters. Inhibition of PHD activity stabilizes hypoxia-inducible factor and other proteins thus acting as a neuroprotective agent. This review will focus on the response of neuronal cells to hypoxia-inducible factor and its targets, including the prolyl hydroxylases. We also present evidence for acute effects of PHD inhibition on synaptic transmission and plasticity in the hippocampus.

Validation of the Fournier's gangrene severity index in a large contemporary series.

PURPOSE: In this study we identified prognostic factors for survival and validated the accuracy of the Fournier's gangrene severity index in patients with Fournier's gangrene. MATERIALS AND METHODS: We retrospectively reviewed medical records of patients diagnosed with Fournier's gangrene between 1996 and 2006. Fournier's gangrene severity index scores were assessed using a receiver operating characteristic curve. Using an outcome variable of inpatient mortality, univariate analyses were performed using the Mann-Whitney U, chi-square and Fisher exact tests. RESULTS: A total of 68 patients (79.4% male, mean age 55.8 +/- 15.2 years) diagnosed with Fournier's gangrene met the criteria for review. The inpatient mortality rate was 10% (7 patients). The mean Fournier's gangrene severity index score for survivors was 5.4 +/- 3.5 vs 10.9 +/- 4.7 for nonsurvivors (p = 0.006). Isolated Fournier's gangrene severity index and individual laboratory parameters associated with mortality included heart rate (p = 0.05), respiratory rate (p = 0.02), serum creatinine (p = 0.03), serum bicarbonate (p = 0.001), serum lactate (p = 0.001) and serum calcium (p = 0.03). Although mean total body surface area was only suggestive of an association (p = 0.169), abdominal wall (p = 0.004) or lower extremity (p = 0.005) involvement was associated with increased mortality. Using a Fournier's gangrene severity index score threshold of 9 (sensitivity 71.4%, specificity 90%) there was a 96% survival rate in patients with a Fournier's gangrene severity index of less than 9 and a 46% mortality rate in those with a Fournier's gangrene severity index of 9 or greater (p = 0.001, OR 22, 95% CI 3.5-139.7). CONCLUSIONS: The Fournier's gangrene severity index remains an objective and simple method to quantify the extent of metabolic aberration at presentation in patients with Fournier's gangrene. A Fournier's gangrene severity index threshold value of 9 is sensitive and specific for predicting mortality in this patient population.

Improved detection of acute parvovirus B19 infection by immunoglobulin M EIA in combination with a novel antigen EIA.

BACKGROUND AND OBJECTIVES: Although parvovirus B19 is a significant blood product contaminant, few methods other than polymerase chain reaction (PCR) have been developed to detect the presence of the virus. MATERIAL AND METHODS: A B19 antigen enzyme immunoassay (EIA) has been developed and the sensitivity of detection is ascertained using dilutions of the B19 capsid protein VP2 and 10-fold dilutions of B19 viraemic serum. Once the assay cut-off was established, a panel of viraemic donations (n = 70) was screened by the antigen EIA. The B19 immunoglobulin M (IgM) and IgG status of these specimens was also determined. During screening of blood donor units by quantitative PCR, 70 individuals were identified with levels of B19 DNA greater than 10(6) IU/ml at the time of blood donation. RESULTS: The sensitivity of the B19 antigen EIA was estimated to be equivalent to between 10(8) and 10(9) IU/ml B19 DNA or 1-10 pg/ml of recombinant capsid protein. B19 detection was significantly enhanced when viraemic specimens were pretreated with a low pH proprietary reagent. Unlike other virus-detection assays, detection of the B19 antigen was not affected by the presence of B19 IgM or IgG antibodies. In addition, the assay was capable of detecting all three genotypes of human erythrovirus. Combined specimen analysis by the B19 antigen assay and a B19 IgM assay facilitated the detection of 91% of acute B19 infections in the test population. CONCLUSION: In combination with B19 IgM detection, application of the B19 antigen EIA is a flexible and efficient method of detecting recent B19 infection and can be used as an alternative to PCR.

Establishment of functional B cell memory against parvovirus B19 capsid proteins may be associated with resolution of persistent infection.

Parvovirus B19 (B19) infection can occur during acute lymphoblastic leukemia and persistent viral infection can occur despite intravenous immunoglobulin administration. Here, evidence is presented that resolution of persistent B19 infection in an acute lymphoblastic leukemia patient may be associated with the simultaneous strengthening of antigen-specific B cell memory against the B19 capsid protein VP2 and diminution in the memory response against the B19 non-structural protein 1 (NS1). Determination of antigen-specific B cell memory status may enhance the serological and molecular analyses of persistent B19 infection.

Evolution of the brain tumour spheroid model: transcending current model limitations.

Tumour recurrence and the high mortality and morbidity associated with malignant brain tumours may be attributed to the failure of current therapeutic modalities (surgery, radiation and chemotherapy) to control the invasion of malignant brain tumour cells into healthy brain tissue. Several in vitro and in vivo models have been developed and used to study brain tumour invasion and cell motility. Here, we review some of the traditional in vitro models of brain tumour invasion and the latest adaptations to the widely used spheroid model. Several research groups studying the mechanisms mediating brain tumour invasion have made important contributions to the field by improving in vitro models of tumour migration and invasion. Sharing these advances will hopefully accelerate experimental discovery and the development of novel anti-invasion brain tumour therapies.

High-sensitivity PCR detection of parvovirus B19 in plasma.

Parvovirus B19 (B19) is a human pathogen transmitted to susceptible individuals via respiratory secretions and contaminated blood or blood products. B19 levels in pooled plasma of less than 10(4) genome equivalents/ml may not be infectious, while those greater than 10(7)/ml are capable of transmitting infection. A World Health Organization (WHO) B19 DNA international standard has been recently introduced. The purpose of the present work was to develop a PCR-enzyme-linked immunosorbent assay (PCR-ELISA) calibrated against the WHO B19 DNA international standard which could easily and reliably detect B19 DNA levels in plasma above 10(4) IU/ml (6.5 x 10(3) genome equivalents/ml). A B19 PCR-ELISA system was developed which uses a dinitrophenylated oligonucleotide probe to detect immobilized biotinylated amplicons following single-round PCR amplification. The level of B19 DNA (in international units per milliliter) in individual and pooled plasma specimens was evaluated. Proteinase K treatment of plasma was found to be sufficient to quantitatively release B19 DNA. The B19 PCR-ELISA had a sensitivity of detection of 1.6 x 10(3) IU/ml B19 DNA and a dynamic range extending from 8 to 1,000 IU of B19 DNA (equivalent to 1.6 x 10(3) to 2 x 10(5) IU of B19 DNA/ml). Furthermore, the antibody profile of pooled plasma products was determined in terms of B19 immunoglobulin G (IgG) (in international units per milliliter). The B19 IgG level was found to be 64.7 +/- 17.5 IU/ml (mean +/- standard deviation). The B19 PCR-ELISA, which is calibrated against the B19 DNA international standard, may have an application for the rapid screening of plasma minipools for B19 DNA, thereby leading to an improvement in blood product safety.

Baculovirus expression of parvovirus B19 (B19V) NS1: utility in confirming recent infection.

BACKGROUND: The presence of anti-parvovirus B19 (B19V) IgM against viral capsid proteins (VP1 and VP2) has long been used to detect recent infection. The utility of antibodies directed against B19V NS1 protein has received less attention as a serological indicator of recent infection, although anti-B19V NS1 IgG has been associated with persistent infection. OBJECTIVES: To elucidate the role of anti-B19V NS1 antibody detection in recent infection, full-length B19V NS1 was expressed and purified. The resultant antigen was used to develop both Western blot assays and microplate ELISA for the detection of NS1 antibodies. STUDY DESIGN: Serum specimens were obtained from individuals recently infected with B19V (children (n=16), adults (n=40)) and from 17 individuals with no evidence of recent B19V infection. All specimens were screened for anti-B19V NS1 IgG and IgM. RESULTS: It was observed that 68.8% (11/16) of children recently infected with B19V were anti-B19V NS1 IgG seropositive. Furthermore, 27.5% (11/40) anti-B19V VP2 IgM positive specimens also contained anti-B19V NS1 IgM when tested by ELISA, while no reactivity was observed following Western blot analysis, possibly due to the absence of conformational epitopes. CONCLUSIONS: Anti-B19V NS1 IgM detection may have utility in the confirmation of recent infection with B19V.

Impaired gamma interferon responses against parvovirus B19 by recently infected children.

Parvovirus B19 is the causative agent of "fifth disease" of childhood. It has been implicated in a variety of conditions, including unsuccessful pregnancy and rheumatoid arthritis, and is a potential contaminant of blood products. There has been little study of immunity to parvovirus B19, and the exact nature of the protective humoral and cell-mediated immune response is unclear. Immune responses to purified virus capsid proteins, VP1 and VP2, were examined from a cohort of recently infected children and compared with responses from long-term convalescent volunteers. The results demonstrate that antibody reactivity is primarily maintained against conformational epitopes in VP1 and VP2. The unique region of VP1 appears to be a major target for cell-mediated immune responses, particularly in recently infected individuals. We confirm that antibody reactivity against linear epitopes of VP2 is lost shortly after infection but find no evidence of the proposed phenotypic switch in either the subclass of parvovirus B19-specific antibody or the pattern of cytokine production by antigen-specific T cells. The dominant subclass of specific antibody detected from both children and adults was immunoglobulin G1. No evidence was found for interleukin 4 (IL-4) or IL-5 production by isolated lymphocytes from children or adults. In contrast, lymphocytes from convalescent adults produced a typical type 1 response associated with high levels of IL-2 and gamma interferon (IFN-gamma). However, we observed a significant (P<0.001) deficit in the production of IFN-gamma in response to VP1 or VP2 from lymphocytes isolated from children. Taken together, these results imply that future parvovirus B19 vaccines designed for children will require the use of conformationally preserved capsid proteins incorporating Th1 driving adjuvants. Furthermore, these data suggest novel mechanisms whereby parvovirus B19 infection may contribute to rheumatoid arthritis and unsuccessful pregnancy.

Minimal tumor necrosis factor receptor binding protein: optimum biological activity of a truncated p55 soluble tumor necrosis factor receptor-IgG fusion protein.

We have previously demonstrated, using expressed deletion constructs, that the fourth membrane proximal cysteine-rich repeat of the p55 TNF receptor (TNF-R) is not required for binding of tumour necrosis factor-alpha (TNF) or lymphotoxin-alpha (LT; tumour necrosis factor-beta). We and others have also shown that the soluble p55 TNF-R, rendered dimeric by fusion to an IgG backbone is extremely effective at neutralizing the harmful effects of TNF overproduction, such as in toxic shock. Here we address the question of how the TNF binding properties of the truncated TNF-R comprising the three distal cysteine-rich repeats (delta4 TNF-R), when fused with an IgG backbone, compare with those of the full length soluble receptor. We constructed several versions of the soluble delta4 TNF-R, on a complete IgG heavy chain backbone and on an IgG lacking the CH1 (first constant region) domain. The constructs were expressed with an Ig or native TNF receptor leader sequence and altered or native N terminal sequence, to compare efficiency of expression. When compared with a full length, soluble receptor Ig fusion protein, the affinity of all for TNF was identical, as were their activities in in vitro binding and cytotoxicity assays. In vivo studies showed that the delta4 and wild type fusion proteins afforded equivalent protection against LPS-induced lethality. However, the delta4 proteins exhibited a significantly lower affinity for LT, and reduced activity in LT binding and cytotoxicity assays. We conclude that the truncated TNF receptor IgG fusion protein is as effective at neutralizing TNF activity as the full length soluble receptor fusion protein. Its lower affinity for LT may make it a more selective agent in blocking the action of TNF, while causing less interference with the action of LT. Also its smaller size may make it a more useful therapeutic agent as it may be less immunogenic than the full length receptor.

Involvement of Brca2 in DNA repair.

Abnormalities precipitated by a targeted truncation in the murine gene Brca2 define its involvement in DNA repair. In culture, cells harboring truncated Brca2 exhibit a proliferative impediment that worsens with successive passages. Arrest in the G1 and G2/M phases is accompanied by elevated p53 and p21 expression. Increased sensitivity to genotoxic agents, particularly ultraviolet light and methylmethanesulfonate, shows that Brca2 function is essential for the ability to survive DNA damage. But checkpoint activation and apoptotic mechanisms are largely unaffected, thereby implicating Brca2 in repair. This is substantiated by the spontaneous accumulation of chromosomal abnormalities, including breaks and aberrant chromatid exchanges. These findings define a function of Brca2 in DNA repair, whose loss precipitates replicative failure, mutagen sensitivity, and genetic instability reminiscent of Bloom syndrome and Fanconi anemia.

Impaired immunoglobulin gene rearrangement in mice lacking the IL-7 receptor.

To generate the full diversity of antibody heavy-chain genes, hundreds of dispersed germline V segments must undergo recombination following D-J segment joining. Here we report that this process is regulated by the alpha-chain of the receptor for interleukin-7, a cytokine that stimulates B-cell lymphopoiesis. D-J joining occurs normally in immature B lymphocytes from mice lacking the alpha-chain of the interleukin-7 receptor (IL-7Ralpha). But recombination of V segments is progressively impaired as their distance increases upstream of D/J, causing infrequent rearrangement of most V segments, which markedly reduces diversity. This is not simply due to defective cell proliferation or impaired recombinase expression. Rather, germline transcripts from distal, unrearranged V segments, a marker of chromatin changes that precede recombination, are specifically silenced. So too is expression of Pax-5, which binds to heavy-chain locus control elements and normally stimulates recombination, suggesting a mechanism for these effects. Thus ligands of the interleukin-7 receptor deliver an extrinsic signal that targets V segment recombination in the heavy-chain locus by altering the accessibility of DNA substrates to the recombinase. This mechanism augments the recombinational diversity of the primary antibody repertoire.

The interleukin-7 receptor alpha chain transmits distinct signals for proliferation and differentiation during B lymphopoiesis.

The interleukin 7 receptor (IL7R), which contains a unique alpha chain and a gamma chain shared by other cytokine receptors, is indispensable for normal lymphocyte development. The basis for this role is poorly understood. Here we show that the IL7R alpha chain not only causes progenitors to proliferate, but also has a distinct activity in inducing differentiation. First, we identify a single cytoplasmic tyrosine residue in the IL7R alpha chain that is essential for cell cycle entry and proliferation dependent on phosphatidylinositol 3-kinase. We use a mutant alpha chain in which this residue has been altered to reconstitute B lymphopoiesis by retrovirus-mediated gene transfer in cultures of bone marrow from mice deficient in IL7R alpha chain. The mutation abrogates the proliferation of B-lymphocyte progenitors, but reveals a novel function of the alpha chain in promoting immunoglobulin heavy chain gene rearrangement leading to B-cell differentiation. This function is lost (but proliferation sustained) when the cytoplasmic domain of IL7R alpha is replaced by corresponding sequences from the IL2R, despite the similarity on their signalling mechanisms. Thus, the signals which mediate a differentiative function of the IL7R in B lymphopoiesis are specific and distinct from those causing proliferation.