Lucas et al. identify humans with a gain-of-function mutation in PIK3R1, encoding the p85α subunit of PI3K. The splice site mutation causes in-frame skipping of exon 11, resulting in altered p85α association with p110δ that stabilizes the catalytic subunit but fails to properly inhibit catalytic activity. The patients have immunodeficiency and lymphoproliferation with skewing of CD8+ T cells toward terminally differentiated and senescent effector cells that have shortened telomeres.

Short-term use of NHF results in a small reduction in PtCO compared with SNP in patients with acute exacerbations of COPD, but whether this is clinically significant is uncertain.

Granulocyte colony-stimulating factor (G-CSF) is the principal cytokine regulating granulopoiesis. G-CSF receptor-deficient mice (G-CSFR-/-) are neutropenic but have only a modest reduction of committed myeloid progenitors. Since it is likely that compensatory mechanisms are induced by the severe neutropenia present in G-CSFR-/- mice, a competitive repopulation assay was performed. These data show that under basal conditions, G-CSF drives nearly all of granulopoiesis through multiple mechanisms. Most importantly, G-CSFR signals regulate the production and/or maintenance of committed-myeloid progenitors. Surprisingly, G-CSFR signals also play a significant role in the regulation of primitive multipotential progenitors in vivo. The contribution of G-CSFR-/- cells to the hematopoietic stem cell compartment is modestly reduced. Moreover, a marked decrease in the contribution of G-CSFR-/- cells to other progenitors in the myeloid pathway, including erythroid and megakaryocytic progenitors, is observed. In contrast, relative to the hematopoietic stem cell compartment, the contribution of G-CSFR-/- cells to the lymphoid lineages is increased. These data suggest that G-CSFR signals may play a role in directing the commitment of primitive hematopoietic progenitors to the common myeloid lineage. Thus, regulation of G-CSF levels may provide a mechanism for directing primitive hematopoietic progenitors into the common myeloid lineage in response to environmental stresses. (Blood. 2003; 102:3562-3568)

Nitric oxide synthase (NOS) catalyzes the conversion of L-arginine to citrulline and nitric oxide (.NO). A baculovirus overexpression system has been developed for a constitutive NOS isoform, cloned originally from rat cerebellum (B-NOS). Recombinant virus was used at a multiplicity of infection of 5 to infect Spodoptera frugiperda cells in culture, and NOS was expressed to 10% of the total soluble protein at 48 h postinfection. In order to express catalytically active enzyme, it was necessary to supplement the culture media with hemin. This increased the activity of the enzyme 7-fold. A two column affinity purification was developed for the recombinant enzyme, which gave homogeneous protein that migrated at 150 kDa on a denaturing polyacrylamide gel. A Km for L-arginine was determined to be 2.0 +/- 0.4 microM. As isolated, recombinant B-NOS exhibited a Soret maximum at 402 nm, which shifted to 394 nm in the presence of L-arginine. The Soret maximum of the reduced enzyme in the presence of CO was 444 nm. Initial rate steady-state kinetic analysis of the recombinant B-NOS showed evidence of substrate inhibition by L-arginine, which could also be seen in a partially purified preparation of B-NOS from rat cerebella. This substrate inhibition was not observed with the inducible isoform of NOS, purified from immunostimulated murine macrophages. A C415H mutant was overexpressed and purified using the same conditions established for the wild-type recombinant B-NOS. This C415H mutant exhibited no activity and did not bind heme, providing the first experimental evidence to support previously reported primary amino acid comparisons which suggest that C415 provides the coordinating thiolate to the heme moiety in B-NOS.