Citations

The protozoan parasite Toxoplasma gondii relies on calcium-mediated exocytosis to secrete adhesins on to its surface where they can engage host cell receptors. Increases in intracellular calcium occur in response to Ins(1,4,5)P3 and caffeine, an agonist of ryanodine-responsive calcium-release channels. We examined lysates and microsomes of T. gondii and detected evidence of cADPR (cyclic ADP ribose) cyclase and hydrolase activities, the two enzymes that control the second messenger cADPR, which causes calcium release from RyR (ryanodine receptor). We also detected endogenous levels of cADPR in extracts of T. gondii. Furthermore, T. gondii microsomes that were loaded with 45Ca2+ released calcium when treated with cADPR, and the RyR antagonists 8-bromo-cADPR and Ruthenium Red blocked this response. Although T. gondii microsomes also responded to Ins(1,4,5)P3, the inhibition profiles of these calcium-release channels were mutually exclusive. The RyR antagonists 8-bromo-cADPR and dantrolene inhibited protein secretion and motility in live parasites. These results indicate that RyR calcium-release channels that respond to the second-messenger cADPR play an important role in regulating intracellular Ca2+, and hence host cell invasion, in protozoan parasites.

Many of the mechanisms that govern T-cell homeostasis remain obscure. Here we report that repeated administration of synthetic oligodeoxynucleotides containing unmethylated cytosine-guanine motifs (CpG-ODN) into mice induces a systemic antigen-independent expansion of naive and memory T cells in a full T-cell compartment. Expansion of T cells was observed on both CD4+ and CD8+ T-cell subsets and was produced not by inducing the proliferation of the cells but by preventing their death. The antiapoptotic effects of CpG-ODN on T cells were observed against activation-induced death and growth factor withdrawal–mediated death. The ability of CpG-ODN to protect T cells from these forms of death was associated with the up-regulation of antiapoptotic gene products including c-FLIP, bcl-xL, and, to some extent, bcl-2. The effect of CpG-ODN on naive and memory T cells required the expression of CD28 and was not dependent on the presence of B lymphocytes, suggesting that other antigen-presenting cells that respond to CpG-ODN, such as dendritic cells, may provide antiapoptotic signals to T cells in an antigen-independent but CD28/B7-dependent fashion. The present findings suggest that CpG-ODN can disrupt normal T-cell homeostasis not by acting as a mitogen but by preventing T-cell death that normally takes place as a mechanism to maintain steady-state levels of T cells. These findings support a potential means to expeditiously replenish and maintain the peripheral lymphocyte population after severe immunodepletion such as that which occurs in HIV-infected individuals and individuals undergoing cytoablative therapies.

Background— Chronobiological rhythms have been shown to influence the occurrence of a variety of cardiovascular disorders. However, the effects of the time of the day, the day of the week, or monthly/seasonal changes on acute aortic dissection (AAD) have not been well studied. Methods and Results— Accordingly, we evaluated 957 patients enrolled in the International Registry of Acute Aortic Dissection (IRAD) between 1996 and 2000 (mean age 62±14 years, type A 61%). A χ 2 test for goodness of fit and partial Fourier analysis were used to evaluate nonuniformity and rhythmicity of AAD during circadian, weekly, and monthly periods. A significantly higher frequency of AAD occurred from 6:00 am to 12:00 noon compared with other time periods (12:00 noon to 6:00 pm , 6:00 pm to 12:00 midnight, and 12:00 midnight to 6:00 am ; P <0.001 by χ 2 test). Fourier analysis showed a highly significant circadian variation ( P <0.001) with a peak between 8:00 am and 9:00 am . Although no significant variation was found for the day of the week, the frequency of AAD was significantly higher during winter ( P =0.008 versus other seasons by χ 2 test). Fourier analysis confirmed this monthly variation with a peak in January ( P <0.001). Subgroup analysis identified a significant association for all subgroups with circadian rhythmicity. However, seasonal/monthly variations were observed only among patients aged <70 years, those with type B AAD, and those without hypertension or diabetes. Conclusions— Similar to other cardiovascular conditions, AAD exhibits significant circadian and seasonal/monthly variations. Our findings may have important implications for the prevention of AAD by tailoring treatment strategies to ensure maximal benefits during the vulnerable periods.

Background: Antibodies to soluble liver antigen/liver pancreas (SLA/LP) are specific markers of autoimmune hepatitis. Their target antigen has recently been cloned. Aims: To establish standardised immunoassays using the recombinant antigen, and to assess the frequency and significance of seropositivity in patients from different countries. Methods: An enzyme linked immunoassay was developed using purified recombinant antigen and validated by testing sera from 200 healthy blood donors and 1026 patients with various liver and non-liver diseases. The assay was then applied to 454 sera from 419 patients with autoimmune hepatitis from different countries. All sera were also tested by inhibition immunoassay and western blot. Results: Antibodies were reliably detected by the recombinant immunoassay and occurred exclusively in patients with autoimmune liver disease. Twenty three of 149 patients from the USA (15%), 23/132 from Brazil (17%), 21/108 from Germany (19%), and 2/30 from Japan (7%) were seropositive. Clinical features at presentation were similar between seropositive and seronegative patients. However, relapse after corticosteroid withdrawal or during maintenance therapy occurred more commonly in seropositive patients. Conclusions: Antibodies to SLA/LP can be reliably detected by these standardised immunoassays based on recombinant antigen. Antibodies to SLA/LP occur with similar frequencies in different geographical regions, races, and age groups, and are of exquisite diagnostic specificity. Whether SLA/LP positive patients represent a clinically distinct subgroup remains to be determined; relapse during treatment reduction appeared to be more common in the SLA/LP group.

Cyclic ADP ribose (cADPR) has been shown to trigger Ca 2+ release from intracellular stores through ryanodine receptor/channel. In our previous study we observed that all- trans- retinoic acid stimulates cADPR synthesis by ADP ribose cyclase (ADPR cyclase) in cultured epithelial cells. We have now investigated whether cADPR may play a signaling role in action of β-estradiol (E 2 ), an archetypal steroid superfamily hormone, upon its major target organ, uterus, in vivo . Administration of E 2 to gonadectomized rats (0.2 mg/kg per day for 7 days) resulted in an ≈Δ + 300% increase of ADPR cyclase activity in extracts from uterus, but in liver, brain, or skeletal muscle ADPR cyclase was unchanged. Most of the E 2 -stimulated uterine ADPR cyclase was associated with membranes. The higher ADPR cyclase activity in response to E 2 was due to the increase of V MAX without change in K m . Simultaneous administration of estrogen antagonist tamoxifen (8 mg/kg per day) with E 2 (0.2 mg/kg per day) prevented an increase in ADPR cyclase. In uterine extracts from E 2 -treated rats, the rate of cADPR inactivation by cADPR hydrolase and the activity of NADase was increased, but to a much lesser degree than activity of ADPR cyclase. Our results indicate that E 2 , via action to its nuclear receptors in vivo , increases ADPR cyclase activity in uterus. We propose that some of the estrogen effects, and by extension the effects of other steroid superfamily hormones, upon specialized cellular functions and upon hormone-induced gene expression in target cells, are mediated by cADPR-Ca 2+ release pathway.