Compound heterozygosity for Pten and SHIP augments T-dependent humoral immune responses and cytokine production by CD(4+) T cells.

Tight regulation of the phosphatidylinositiol 3-kinase (PI3K) pathway is essential not only for normal immune system development and responsiveness, but also in the prevention of immunopathology. Indeed, unchecked activation of the PI3K pathway in T cells induces lymphoproliferation and systemic autoimmunity. Evaluating the importance of threshold levels of two key PI3K pathway phosphoinositol phosphatases, we previously reported that mice heterozygous for both Pten and SHIP develop a more rapid progression of a lymphoproliferative autoimmune syndrome than do Pten(+\-) mice. Investigating the basis for this difference, we now describe a quantitative and qualitative difference in the antibody responses of C57BL\6 Pten(+\-) SHIP(+\-) mice upon challenge with a T-dependent antigen. Suspecting that this phenotypic difference might be the result, at least in part, of a T-helper cell defect, an in vitro analysis of anti-CD3/interleukin (IL)-2-expanded CD4(+) T cells was performed. After stimulation with anti-CD3, cells from mice heterozygous for both Pten and SHIP exhibited a striking increase in IL-4 secretion (> 10-fold), without a corresponding increase in T helper 2 (Th2) cell numbers being evident by intracellular staining for this cytokine. Modest increases were also seen for both IL-13 and IFN-gamma. Perhaps in keeping with this abnormal in vitro cytokine profile, IgG1 serum levels were significantly elevated in young C57BL\6 Pten(+\-) SHIP(+\-) mice. Thus, the relative levels of Pten and SHIP appear to be key variables in CD4(+) T-cell function, primarily via their ability to regulate IL-4 production.

Loss of a single allele of SHIP exacerbates the immunopathology of Pten heterozygous mice.

Phosphatidylinositol 3-kinase (PI3K) has emerged as a critical component of multiple immune system intracellular signalling pathways. The levels and relative ratios of PI3K products, phosphatidylinositol (3,4) bisphosphate (PI(3,4)P(2)) and phosphatidylinositol (3,4,5) trisphosphate (PIP(3)), are regulated by inositol phosphatases such as Pten and SHIP. Interestingly, mice heterozygous for Pten, a 3'-inositol phosphatase, develop a progressive lymphoproliferative syndrome with autoimmune features. Given the importance of PIP(3) species in regulating immune responses, we hypothesized that heterozygosity for the 5'-inositol phosphatase SHIP might exacerbate the autoimmune phenotype of Pten(+/-) mice. In keeping with this, mice heterozygous for both Pten and SHIP developed lymphoproliferation, hypergammaglobulinaemia, autoantibody titres and renal pathology that were more severe than that of Pten(+/-) mice. These results suggest that the relative levels of phosphatidylinositol phosphatases are likely critical to immune system homeostasis and they also highlight the potential for gene dosage effects in regulating susceptibility and/or severity of autoimmunity.

Universality of mitochondrial RNA editing in cytochrome-c oxidase subunit I (coxI) among the land plants.

Plant mitochondrial pre-mRNAs often undergo C-to-U conversions, a phenomenon termed RNA editing. The molecular source of specificity and phylogenetic depth of the editing machinery remain to be determined. We amplified coxI gene fragments via the polymerase chain reaction from a diversity of taxa within the land plants, and sequenced each. Alignment and comparison of 25 homologous coxI gene sequences with those from plant species having known RNA editing sites which restore amino acid sequence consensus was used to infer sites of C-to-U conversions. Our results, derived using the comparative approach, imply that the plant mitochondrial editing machinery extends throughout vascular plant phylogeny, and also that this phenomenon is present in every major branch of the (non-vascular) Bryophyta: liverworts (Hepaticae), hornworts (Anthocerotae), and mosses (Musci). These results have important consequences for our thoughts on the evolutionary history of the plant RNA editing process, as they imply that editing is older than was previously believed.

Muscle spasms associated with ear tick (Otobius megnini) infestations in five horses.

Severe muscle cramping not associated with exercise was observed in 5 horses. Focal muscle groups in various regions underwent intermittent visible contraction. Intermittent prolapse of the third eyelid, sweating, pawing, muscle tremors, and muscle fasciculations also were observed. Clinical signs often were misconstrued as signs of colic. Percussion of muscle induced contraction of muscle groups. Concentrations of serum electrolytes and the acid-base balance were within reference limits, but activities of creatine kinase and aspartate transaminase were moderately high. Muscle biopsy revealed no abnormalities except for a few necrotic muscle fibers undergoing phagocytosis. Electromyography of 1 horse was suggestive of increased motor unit activity. All horses had Otobius megnini (ear tick) infestations and had recurrence of signs until treatment was initiated for ear ticks.