PI3Kδ and primary immunodeficiencies.

Primary immunodeficiencies are inherited disorders of the immune system, often caused by the mutation of genes required for lymphocyte development and activation. Recently, several studies have identified gain-of-function mutations in the phosphoinositide 3-kinase (PI3K) genes PIK3CD (which encodes p110δ) and PIK3R1 (which encodes p85α) that cause a combined immunodeficiency syndrome, referred to as activated PI3Kδ syndrome (APDS; also known as p110δ-activating mutation causing senescent T cells, lymphadenopathy and immunodeficiency (PASLI)). Paradoxically, both loss-of-function and gain-of-function mutations that affect these genes lead to immunosuppression, albeit via different mechanisms. Here, we review the roles of PI3Kδ in adaptive immunity, describe the clinical manifestations and mechanisms of disease in APDS and highlight new insights into PI3Kδ gleaned from these patients, as well as implications of these findings for clinical therapy

ATM Limits Incorrect End Utilization during Non-Homologous End Joining of Multiple Chromosome Breaks

Chromosome rearrangements can form when incorrect ends are matched during end joining (EJ) repair of multiple chromosomal double-strand breaks (DSBs). We tested whether the ATM kinase limits chromosome rearrangements via suppressing incorrect end utilization during EJ repair of multiple DSBs. For this, we developed a system for monitoring EJ of two tandem DSBs that can be repaired using correct ends (Proximal-EJ) or incorrect ends (Distal-EJ, which causes loss of the DNA between the DSBs). In this system, two DSBs are induced in a chromosomal reporter by the meganuclease I-SceI. These DSBs are processed into non-cohesive ends by the exonuclease Trex2, which leads to the formation of I-SceI–resistant EJ products during both Proximal-EJ and Distal-EJ. Using this method, we find that genetic or chemical disruption of ATM causes a substantial increase in Distal-EJ, but not Proximal-EJ. We also find that the increase in Distal-EJ caused by ATM disruption is dependent on classical non-homologous end joining (c-NHEJ) factors, specifically DNA-PKcs, Xrcc4, and XLF. We present evidence that Nbs1-deficiency also causes elevated Distal-EJ, but not Proximal-EJ, to a similar degree as ATM-deficiency. In addition, to evaluate the roles of these factors on end processing, we examined Distal-EJ repair junctions. We found that ATM and Xrcc4 limit the length of deletions, whereas Nbs1 and DNA-PKcs promote short deletions. Thus, the regulation of end processing appears distinct from that of end utilization. In summary, we suggest that ATM is important to limit incorrect end utilization during c-NHEJ

Clinical spectrum and features of activated phosphoinositide 3-kinase δ syndrome: A large patient cohort study

Background: Activated PI3-Kinase Delta Syndrome (APDS) is a recently described combined immunodeficiency resulting from gain-of-function mutations in PIK3CD, the gene encoding the catalytic subunit of phosphoinositide 3-kinase δ (PI3Kδ). Objective: To review the clinical, immunological, histopathological and radiological features of APDS in a large genetically-defined international cohort. Methods: Clinical questionnaire, and review of medical notes, radiology histopathology and laboratory investigations of 53 APDS patients. Results: Recurrent sino-pulmonary infections (96%) and non-neoplastic lymphoproliferation (75%) were common, often from childhood. Other significant complications included herpesvirus infections (49%), autoinflammatory disease (34%), and lymphoma (13%). Unexpectedly, neurodevelopmental delay occurred in 19% of the cohort, suggesting a role for PI3Kδ in the central nervous system (CNS); consistent with this PI3Kδ is broadly expressed in the developing murine CNS. Thoracic imaging revealed high rates of mosaic attenuation (90%) and bronchiectasis (60% in cohort); the incidence of bronchiectasis was greater than in common variable immunodeficiency (CVID). Elevated IgM (78%), IgG deficiency (43%) and CD4 lymphopenia (84%) were significant immunological features. No immunological marker reliably predicted clinical severity, which ranged from asymptomatic to death in early childhood. The majority of patients received immunoglobulin replacement and antibiotic prophylaxis, and five patients underwent haematopoietic stem cell transplant (HSCT). Five patients died from complications of APDS. Conclusion: APDS is a combined immunodeficiency with multiple clinical manifestations, many with incomplete penetrance and others with variable expressivity. The severity of complications in some patients supports consideration of HSCT for severe childhood disease. Clinical trials of selective PI3Kδ inhibitors offer new prospects for APDS treatment

Sintered Alpha Silicon Carbide Pump Bearings - Tribological Materials Optimization To Improve Reliability

Lecturepg. 63The material properties of sintered silicon carbide, such as universal corrosion resistance, hardness, strength, and thermal conductivity, offer a great potential as sealless pump bearings and mechanical seal faces. In order to exploit the positive properties of pure silicon carbide, one also has to deal with its most negative property, brittleness. The brittleness requires knowledgeable ceramic design combined with appropriate material properties as the necessary requirements for reliable performance of a ceramic component. Both materials properties and design features are discussed with regard to the successful application of sintered silicon carbide as sealless pump bearings

Impaired induction of DNA lesions during immunoglobulin class-switch recombination in humans influences end-joining repair

Ig class-switch recombination (CSR) is a region-specific process that exchanges the constant Ig heavy-chain region and thus modifies an antibody's effector function. DNA lesions in switch (S) regions are induced by activation-induced cytidine deaminase (AID) and uracil-DNA glycosylase 2 (UNG2), subsequently processed to DNA breaks, and resolved by either the classical nonhomologous end-joining pathway or the alternative end-joining pathway (XRCC4/DNA ligase 4– and/or Ku70/Ku80-independent and prone to increased microhomology usage). We examined whether the induction of DNA lesions influences DNA end-joining during CSR by analyzing Sμ–Sα recombination junctions in various human Ig CSR defects of DNA lesion induction. We observed a progressive trend toward the usage of microhomology in Sμ–Sα recombination junctions from AID-heterozygous to AID–autosomal dominant to UNG2-deficient B lymphocytes. We thus hypothesize that impaired induction of DNA lesions in S regions during CSR leads to unusual end-processing of the DNA breaks, resulting in microhomology-mediated end-joining, which could be an indication for preferential processing by alternative end-joining rather than by classical nonhomologous end-joining