Functional plasticity of regulatory T cells (168.7)

Regulatory T cells (Tregs) play a pivotal role in maintaining immune homeostasis, preventing autoimmunity, controlling exaggerated immune responses against infections and suppressing anti-tumor immunity. Tregs utilize multiple mechanisms to mediate their function. However, the number of mechanisms critical to exert maximal suppressive activity is unclear. It is conceivable that suppressive mechanisms could be tightly regulated by cross-regulatory networks. It has been shown that interleukin 10 (IL10) and IL35 have critical role in Treg function. Therefore, we assessed the functional capacity of Tregs lacking the ability to secrete IL10 and IL35. Surprisingly, our study revealed that Tregs lacking both IL10 and IL35 (Ebi3-/-Il10-/- or Il12a-/-Il10-/-) were fully functional and were able to suppress Tconv cells both in vitro and in vivo . Absence of IL10 and IL35 was compensated by an increase in cathepsin E (CTSE), influencing the release of soluble TRAIL and thereby resulting in suppression of target cells in a TRAIL-dependent manner. Inhibiting TRAIL activity disrupted the function of Ebi3-/-Il10-/- Tregs. The loss of suppressive function was maximal in Tregs lacking IL10, IL35 and TRAIL (Ebi3-/-Il10-/-Tnfsf10-/-Tregs). These data suggests the existence of cross-regulatory networks which controls the utilization of suppressive factors, thereby maintaining Treg functional plasticity.

A single episode of haematospermia can be safely managed in the community

INTRODUCTION

This study is a ten-year single institution retrospective study of patients presenting with haematospermia, to establish standard tests for investigation, and what tests have low yield and can be omitted.

MATERIALS AND METHODS

Investigations that were used were analysed to establish their diagnostic yield. The parameters examined were: digital rectal examination (DRE) findings, prostate specific antigen (PSA), abdominal and scrotal ultrasound, TRUS biopsy result (wherever applicable), flexible cystoscopy findings and final diagnosis.

RESULTS

The central findings were that abdominal ultrasound never yielded an abnormality and that flexible cystoscopy never showed bladder tumours. TRUS prostate biopsies were performed in 17% of patients, and prostate cancer was confirmed in 5% of patients. Testicular malignancy was found in 2%. In 90% of patients, no specific diagnosis was made, and 85% of patients were discharged at review.

CONCLUSIONS

A single episode of haematospermia is usually benign. Flexible cystoscopy and abdominal ultrasound appear valueless. Assessment should consist of clinical examination (including testicular), DRE and PSA testing. It can safely be managed in the community and only referred in the presence of, abnormal examination, elevated PSA or recurrent symptoms.

Medical ethics and law for doctors of tomorrow: the 1998 Consensus Statement updated

Knowledge of the ethical and legal basis of medicine is as essential to clinical practice as an understanding of basic medical sciences. In the UK, the General Medical Council (GMC) requires that medical graduates behave according to ethical and legal principles and must know about and comply with the GMC's ethical guidance and standards. We suggest that these standards can only be achieved when the teaching and learning of medical ethics, law and professionalism are fundamental to, and thoroughly integrated both vertically and horizontally throughout, the curricula of all medical schools as a shared obligation of all teachers. The GMC also requires that each medical school provides adequate teaching time and resources to achieve the above. We reiterate that the adequate provision and coordination of teaching and learning of ethics and law requires at least one full-time senior academic in ethics and law with relevant professional and academic expertise. In this paper we set out an updated indicative core content of learning for medical ethics and law in UK medical schools and describe its origins and the consultative process by which it was achieved.

The receptor S1P1 overrides regulatory T cell-mediated immune suppression through Akt-mTOR

Regulatory T cells (T_reg) are critically involved in maintaining immunological tolerance, but this potent suppression must be quenched to allow the generation of adaptive immune responses. Here we report that type 1 sphingosine-1-phosphate (S1P) receptor (S1P₁) delivers an intrinsic negative signal to restrain thymic generation, peripheral maintenance and suppressive activity of T_reg cells. Combining loss- and gain-of-function genetic approaches, we found that S1P₁ blocked the differentiation of thymic T_reg precursors and function of mature Treg cells, and affected T_reg-mediated immune tolerance. S1P₁ induced the selective activation of the Akt-mTOR pathway to impede T_reg development and function. Dynamic regulation of S1P₁ contributed to lymphocyte priming and immune homeostasis. Thus, by antagonizing T_reg-mediated immune suppression, the lipid-activated S1P₁-Akt-mTOR pathway orchestrates adaptive immune responses.

A mouse model for glucocorticoid-induced osteonecrosis: effect of a steroid holiday

Glucocorticoid-induced osteonecrosis is a common and dose-limiting adverse event. The goal of this study was to establish a mouse model of glucocorticoid-induced osteonecrosis suitable for testing the effects of different treatment strategies on its frequency. Fourteen murine strains were screened using various glucocorticoids, routes of administration, and diets. Four-week-old male BALB/cJ mice were treated with oral dexamethasone for up to 12 weeks either by continuous dosing or by discontinuous dosing, with or without asparaginase. Histopathological features of the distal femurs were examined by light microscopy. Osteonecrotic lesions were characterized by empty lacunae and osteocyte ghosts in trabecular bone surrounded by necrotic marrow and edema. The incidence of dexamethasone induced osteonecrosis in BALB/cJ mice was 40-45% (4/10 or 5/11) at 12 weeks. The frequency of osteonecrosis trended lower after discontinuous compared to continuous dosing for 12 weeks (8 vs. 45%) (p = 0.06) despite comparable cumulative plasma exposure. Asparaginase hastened the occurrence of osteonecrosis, which was observed as early as 4 weeks and the incidence was 50% after 6 weeks. A mouse model of glucocorticoid-induced osteonecrosis was established. Discontinuous was less osteonecrotic than continuous dexamethasone treatment, consistent with the possible benefits of a "steroid holiday" seen in clinical settings. Moreover, asparaginase hastened osteonecrosis, indicating that drugs may interact with glucocorticoids to affect osteonecrosis risk.

Clarithromycin with low dose dexamethasone and thalidomide is effective therapy in relapsed/refractory myeloma

A combination of clarithromycin, low dose of thalidomide and low dose dexamethasone was used in a phase II study to treat patients with relapsed and refractory myeloma. Thirty patients received clarithromycin 250 mg twice daily and thalidomide 50 mg at night on an ongoing basis with 4-d pulses of 10 mg dexamethasone given monthly. Eight patients had permitted escalation of thalidomide dosage up to 200 mg daily. The combination was well tolerated and could be given to elderly, infirm and severely cytopenic patients. Response rates were high, with 89% achieving at least 50% reduction in paraprotein and a 96% overall response rate. Although clarithromycin has only minimal anti-myeloma properties when used as a single agent, its combination with thalidomide and dexamethasone appears very effective, allowing these to be used in lower and more tolerable doses with good clinical effects.

Transporter-mediated protection against thiopurine-induced hematopoietic toxicity

Thiopurines are effective immunosuppressants and anticancer agents, but intracellular accumulation of their active metabolites (6-thioguanine nucleotides, 6-TGN) causes dose-limiting hematopoietic toxicity. Thiopurine S-methyltransferase deficiency is known to exacerbate thiopurine toxicity. However, many patients are highly sensitive to thiopurines for unknown reasons. We show that multidrug-resistance protein 4 (Mrp4) is abundant in myeloid progenitors and tested the role of the Mrp4, an ATP transporter of monophosphorylated nucleosides, in this unexplained thiopurine sensitivity. Mrp4-deficient mice experienced Mrp4 gene dosage-dependent toxicity caused by accumulation of 6-TGNs in their myelopoietic cells. Therefore, Mrp4 protects against thiopurine-induced hematopoietic toxicity by actively exporting thiopurine nucleotides. We then identified a single-nucleotide polymorphism (SNP) in human MRP4 (rs3765534) that dramatically reduces MRP4 function by impairing its cell membrane localization. This SNP is common (>18%) in the Japanese population and indicates that the increased sensitivity of some Japanese patients to thiopurines may reflect the greater frequency of this MRP4 SNP.

Cytokine secretion requires phosphatidylcholine synthesis

Choline cytidylyltransferase (CCT) is the rate-limiting enzyme in the phosphatidylcholine biosynthetic pathway. Here, we demonstrate that CCTα-mediated phosphatidylcholine synthesis is required to maintain normal Golgi structure and function as well as cytokine secretion from the Golgi complex. CCTα is localized to the trans-Golgi region and its expression is increased in lipopolysaccharide (LPS)-stimulated wild-type macrophages. Although LPS triggers transient reorganization of Golgi morphology in wild-type macrophages, similar structural alterations persist in CCTα-deficient cells. Pro–tumor necrosis factor α and interleukin-6 remain lodged in the secretory compartment of CCTα-deficient macrophages after LPS stimulation. However, the lysosomal-mediated secretion pathways for interleukin-1β secretion and constitutive apolipoprotein E secretion are unaltered. Exogenous lysophosphatidylcholine restores LPS-stimulated secretion from CCTα-deficient cells, and elevated diacylglycerol levels alone do not impede secretion of pro–tumor necrosis factor α or interleukin-6. These results identify CCTα as a key component in membrane biogenesis during LPS-stimulated cytokine secretion from the Golgi complex.

Transplantable marrow osteoprogenitors engraft in discrete saturable sites in the marrow microenvironment

OBJECTIVE

Based on the recognition that marrow contains progenitors for bone as well as blood, we undertook the first trial of bone marrow transplantation (BMT) for a genetic disorder of bone, osteogenesis imperfecta. While we documented striking clinical benefit soon after transplantation, the measured level of osteopoietic engraftment was low. To improve the efficacy of BMT for bone disorders, we sought to gain insight into the cellular mechanism of engraftment of transplantable marrow osteoprogenitors.

MATERIALS AND METHODS

We transplanted unfractionated bone marrow harvested from green fluorescent protein-transgenic FVB/N mice into lethally irradiated FVB/N recipients. At 3 weeks posttransplantation, we assessed hematopoietic engraftment by flow cytometry and osteopoietic engraftment by immunohistochemical staining for the green fluorescent protein.

RESULTS

We show that engraftment of transplantable marrow osteoprogenitors is saturable with a maximal engraftment of about 15% of all bone cells in the epiphysis and metaphysis of the femur at 3 weeks after transplantation. The number of engrafting sites is not up- or downregulated in response to initial progenitor cell engraftment, and there is no evidence for clonal succession of osteopoietic differentiation of engrafted progenitors.

CONCLUSIONS

Our findings indicate that the capacity for initial osteopoietic engraftment after BMT is limited and "megadose" stem cell transplantation is unlikely to enhance engraftment. Thus, novel strategies to foster osteopoietic chimerism must be developed.