Cell-mediated immunity in Cryptococcosis

Cell-mediated immune responses in patients who had recovered from cryptococcosis were compared to those of healthy subjects. Cryptococcal patients were mildly lymphopenic but showed no defect in percentage of thymus-derived lymphocytes. One-third had positive delayed skin test reactions to cryptococcal antigen. Their skin test reactivity to two commonly used noncryptococcal antigens was less intense than healthy control subjects. Strongly positive and specific lymphocyte transformation occurred in the presence of an extract of Cryptococcus neoformans (cryptococcin) in half of the patients. In contrast, few healthy subjects had positive transformation responses to cryptococcin. One patient who was followed sequentially through treatment of cryptococcal meningitis acquired strong cryptococcin reactivity during the course of treatment. Cellular immunologic response to cryptococcin identifies many subjects who have had C. neoformans exposure, and may be of value for assessing immunologic status of patients undergoing therapy. These studies also indicate that most patients with cryptococcosis have a degree of deficiency in cell-mediated response to fungal antigens even when a specific underlying disease process cannot be identified.     

Plasma neurotensin release and gastric emptying in the dumping syndrome

Seventy-three patients were studied after ingesting a liquid glucose meal, tagged with ¹¹³Indium. Nineteen of these patients were awaiting surgery for their duodenal ulcer, while 54 were studied postoperatively, 25 of whom experienced troublesome postprandial (dumping) symptoms in their daily lives. The radioactive marker emptied significantly faster in the symptomatic patients than in the symptomfree, pre and post-operative groups (initial emptying rate 3.45 ± 0.23, compared with 1.16 ± 0.19 and 1.27 ± 0.15% fall in counts/min respectively; p < 0.01). Initial (20 min) rises in the plasma concentrations of neurotensin-like immunoreactivity measured during the test correlated significantly with the rate of gastric emptying in all patients, being greatest in patients with dumping symptoms. Physiological concentrations of neurotensin have been shown to delay gastric emptying. The excessive rise in plasma neurotensin-like immunoreactivity in patients with dumping symptoms, presumably occuring as a result of the rapid passage of nutrients to the neurotensin-rich ileum, may possibly have a compensatory role in slowing further emptying from the stomach.     

Conotoxin GI: disulfide bridges, synthesis, and preparation of iodinated derivatives

The 13 amino acid toxic peptide from the marine snail Conus geographus, conotoxin GI, blocks the acetylcholine receptor at the neuromuscular junction. In this report, we describe a method for analyzing disulfide bonding in nanomole amounts of small cystine-rich peptides. The procedure involves partial reduction and a double-label alkylation of cysteine residues. Using this method, we show that the natural conotoxin GI has a (2-7, 3-13) disulfide configuration. The structure of conotoxin GI has been confirmed by chemical synthesis. The preparation and purification of molecularly homogeneous, iodinated derivatives of this toxin are also described. All derivatives, including the [diiodohistidine,diiodotyrosine]conotoxin GI, retained at least half of the biological activity of unmodified toxin. Since the tetraiodinated toxin, which is greater than 25% by weight iodine, retains considerable toxicity, unmodified histidine and tyrosine residues in conotoxin GI are not crucial for biological activity.     

Effect of food deprivation and hypophysectomy on in vitro protein synthesis by membrain-bound and free hepatic ribosomes.

The protein synthetic activities of membrane-bound and free hepatic ribosomes isolated from intact rats fed ad libitum, and normal rats subjected to food restriction to match that of hypophysectomised (Hx) rats were compared to the in vitro protein synthetic capacity of hepatic ribosomes isolated from Hx rats. Hypophysectomy resulted in decreased protein synthetic ability of bound ribosomes, whether protein synthesis was directed by endogenous messenger RNA (mRNA) (p less than 0.05) or by polyuridylic acid (polyU) (p less than 0.01). In contrast, the protein synthetic activity of free hepatic ribosomes from Hx rats was reduced when protein synthesis was directed by endogenous mRNA (p less than 0.05) but, when polyU was substituted as the messenger, the protein synthetic activity of these free ribosomes was equal to that of control rats. On the other hand the effects of food restriction on hepatic ribosomal function could be clearly differentiated from the effects observed following hypophysectomy. Thus, the reduced protein synthetic activity of hepatic bound ribosomes isolated from food restricted normal rats was not demonstrable, when polyU was used to direct protein synthesis. Further, food restriction had no effect on the protein synthetic activity of free hepatic ribosomes, and this was true when protein synthesis was directed by either endogenous or artificial messenger. It is concluded that hypophysectomy reduces the protein synthetic ability of both bound and free hepatic ribosomes, and this change of ribosomal function of Hx rats cannot be attributed to their decreased food intake.     

The return of the frogs: The importance of habitat refugia in maintaining diversity during a disease outbreak

Recent decades have seen the emergence and spread of numerous infectious diseases, often with severe negative consequences for wildlife populations. Nevertheless, many populations survive the initial outbreaks, and even undergo recoveries. Unfortunately, the long‐term effects of these outbreaks on host population genetics are poorly understood; to increase this understanding, we examined the population genetics of two species of rainforest frogs (Litoria nannotis and Litoria serrata) that have largely recovered from a chytridiomycosis outbreak at two national parks in the Wet Tropics of northern Australia. At the wetter, northern park there was little evidence of decreased genetic diversity in either species, and all of the sampled sites had high minor allele frequencies (mean MAF = 0.230–0.235), high heterozygosity (0.318–0.325), and few monomorphic markers (1.4%–4.0%); however, some recovered L. nannotis populations had low N_e values (59.3–683.8) compared to populations that did not decline during the outbreak (1,537.4–1,756.5). At the drier, southern park, both species exhibited lower diversity (mean MAF = 0.084–0.180; heterozygosity = 0.126–0.257; monomorphic markers = 3.7%–43.5%; N_e = 18.4–676.1). The diversity patterns in this park matched habitat patterns, with both species having higher diversity levels and fewer closely related individuals at sites with higher quality habitat. These patterns were more pronounced for L. nannotis, which has lower dispersal rates than L. serrata. These results suggest that refugia with high quality habitat are important for retaining genetic diversity during disease outbreaks, and that gene flow following disease outbreaks is important for re‐establishing diversity in populations where it was reduced.     

Linking fish trait responses to in‐stream habitat in reconstructed valley‐plugged stream reaches of the Coastal Plain,U.S.A.

Valley‐plug formation is a challenging consequence of stream channelization especially in physiographic regions with highly erodible soils. Upstream channel degradation and incision results in accelerated sediment delivery processes wherein downstream aggradation decreases stream power and creates sand‐clogged channels. Channel reconstruction is now meeting hydrogeomorphic goals related to valley‐plug remediation, yet there exists a need to understand how this practice also facilitates ecological restoration. We evaluated fish trait response to in‐stream habitat conditions in channelized, recently restored, and “least‐disturbed” reference reaches of Coastal Plain streams in West Tennessee. Restored reaches were ecologically similar to channelized reaches, having higher proportions of nest‐guarding omnivores that were correlated with higher percentages of pool habitats and lower wetted width:depth ratios compared to reference reaches. Reference reaches had higher proportions of fast‐water dwelling and specialized insectivores that were correlated with high abundance of large woody debris, high‐wetted width:depth ratios, and low percentages of pool habitats. We conclude that in‐stream habitats in reconstructed channels have yet to promote reach‐scale ecological restoration relative to fish assemblage organization because trait‐habitat associations were not similar to reference conditions. However, our results lend to the development of ecological restoration targets that can be incorporated in future channel reconstruction projects in valley‐plugged, channelized streams of the Coastal Plain.     

Common molecular pathways involved in human CD133+/CD34+ progenitor cell expansion and cancer

Background  

Uncovering the molecular mechanism underlying expansion of hematopoietic stem and progenitor cells is critical to extend current therapeutic applications and to understand how its deregulation relates to leukemia. The characterization of genes commonly relevant to stem/progenitor cell expansion and tumor development should facilitate the identification of novel therapeutic targets in cancer.     

Resistance to chytridiomycosis varies among amphibian species and is correlated with skin peptide defenses

Innate immune mechanisms of defense are especially important to ectothermic vertebrates in which adaptive immune responses may be slow to develop. One innate defense in amphibian skin is the release of abundant quantities of antimicrobial peptides. Chytridiomycosis is an emerging infectious disease of amphibians caused by the skin fungus, Batrachochytrium dendrobatidis . Susceptibility to chytridiomycosis varies among species, and mechanisms of disease resistance are not well understood. Previously, we have shown that Australian and Panamanian amphibian species that possess skin peptides that effectively inhibit the growth of B. dendrobatidis in vitro tend to survive better in the wild or are predicted to survive the first encounter with this lethal pathogen. For most species, it has been difficult to experimentally infect individuals with B. dendrobatidis and directly evaluate both survival and antimicrobial peptide defenses. Here, we demonstrate differences in susceptibility to chytridiomycosis among four Australian species ( Litoria caerulea, Litoria chloris, Mixophyes fasciolatus and Limnodynastes tasmaniensis ) after experimental infection with B. dendrobatidis , and show that the survival rate increases with the in vitro effectiveness of the skin peptides. We also observed that circulating granulocyte, but not lymphocyte, counts differed between infected and uninfected Lit. chloris . This suggests that innate granulocyte defenses may be activated by pathogen exposure. Taken together, our data suggest that multiple innate defense mechanisms are involved in resistance to chytridiomycosis, and the efficacy of these defenses varies by amphibian species.     

Context-dependent symbioses and their potential roles in wildlife diseases

It is well known in ecology, evolution and medicine that both the nature (commensal, parasitic and mutualistic) and outcome (symbiont fitness, survival) of symbiotic interactions are often context-dependent. Less is known about the importance of context-dependence in symbioses involved in wildlife disease. We review variable symbioses, and use the amphibian disease chytridiomycosis to demonstrate how understanding context-dependence can improve the understanding and management of wildlife diseases. In chytridiomycosis, the host-pathogen interaction is context-dependent; it is strongly affected by environmental temperature. Skin bacteria can also modify the interaction; some bacteria reduce amphibians' susceptibility to chytridiomycosis. Augmentation of protective microbes is being considered as a possible management tool, but informed application of bioaugmentation requires understanding of how the interactions between host, beneficial bacteria and pathogen depend upon environmental context. The community-level response of the amphibian skin microbiota to environmental conditions may explain the relatively narrow range of environmental conditions in which past declines have occurred. Environmental context affects virulence and the protection provided by mutualists in other host-pathogen systems, including threatened bats and corals. Increased focus on context-dependence in interactions between wildlife and their symbionts is likely to be crucial to the future investigation and management of emerging diseases of wildlife.