Teleost intestinal immunology

Teleosts clearly have a more diffuse gut associated lymphoid system, which is morphological and functional clearly different from the mammalian GALT. All immune cells necessary for a local immune response are abundantly present in the gut mucosa of the species studied and local immune responses can be monitored after intestinal immunization. Fish do not produce IgA, but a special mucosal IgM isotype seems to be secreted and may (partly) be the recently described IgZ/IgT. Fish produce a pIgR in their mucosal tissues but it is smaller (2 ILD) than the 4–5 ILD pIgR of higher vertebrates. Whether teleost pIgR is transcytosed and cleaved off in the same way needs further investigation, especially because a secretory component (SC) is only reported in one species. Teleosts also have high numbers of IEL, most of them are CD3-?⁺/CD8-α⁺ and have cytotoxic and/or regulatory function. Possibly many of these cells are TCRγδ cells and they may be involved in the oral tolerance induction observed in fish. Innate immune cells can be observed in the teleost gut from first feeding onwards, but B cells appear much later in mucosal compartments compared to systemic sites. Conspicuous is the very early presence of putative T cells or their precursors in the fish gut, which together with the rag-1 expression of intestinal lymphoid cells may be an indication for an extra-thymic development of certain T cells. Teleosts can develop enteritis in their antigen transporting second gut segment and epithelial cells, IEL and eosinophils/basophils seem to play a crucial role in this intestinal inflammation model. Teleost intestine can be exploited for oral vaccination strategies and probiotic immune stimulation. A variety of encapsulation methods, to protect vaccines against degradation in the foregut, are reported with promising results but in most cases they appear not to be cost effective yet. Microbiota in fish are clearly different from terrestrial animals. In the past decade a fast increasing number of papers is dedicated to the oral administration of a variety of probiotics that can have a strong health beneficial effect, but much more attention has to be paid to the immune mechanisms behind these effects. The recent development of gnotobiotic fish models may be very helpful to study the immune effects of microbiota and probiotics in teleosts.     

GPI-anchored proteins are directly targeted to the apical surface in fully polarized MDCK cells

The polarity of epithelial cells is dependent on their ability to target proteins and lipids in a directional fashion. The trans-Golgi network, the endosomal compartment, and the plasma membrane act as sorting stations for proteins and lipids. The site of intracellular sorting and pathways used for the apical delivery of glycosylphosphatidylinositol (GPI)-anchored proteins (GPI-APs) are largely unclear. Using biochemical assays and confocal and video microscopy in living cells, we show that newly synthesized GPI-APs are directly delivered to the apical surface of fully polarized Madin-Darby canine kidney cells. Impairment of basolateral membrane fusion by treatment with tannic acid does not affect the direct apical delivery of GPI-APs, but it does affect the organization of tight junctions and the integrity of the monolayer. Our data clearly demonstrate that GPI-APs are directly sorted to the apical surface without passing through the basolateral membrane. They also reinforce the hypothesis that apical sorting of GPI-APs occurs intracellularly before arrival at the plasma membrane.     

Cell-cycle inhibition by Helicobacter pylori L-asparaginase

Helicobacter pylori (H. pylori) is a major human pathogen causing chronic gastritis, peptic ulcer, gastric cancer, and mucosa-associated lymphoid tissue lymphoma. One of the mechanisms whereby it induces damage depends on its interference with proliferation of host tissues. We here describe the discovery of a novel bacterial factor able to inhibit the cell-cycle of exposed cells, both of gastric and non-gastric origin. An integrated approach was adopted to isolate and characterise the molecule from the bacterial culture filtrate produced in a protein-free medium: size-exclusion chromatography, non-reducing gel electrophoresis, mass spectrometry, mutant analysis, recombinant protein expression and enzymatic assays. L-asparaginase was identified as the factor responsible for cell-cycle inhibition of fibroblasts and gastric cell lines. Its effect on cell-cycle was confirmed by inhibitors, a knockout strain and the action of recombinant L-asparaginase on cell lines. Interference with cell-cycle in vitro depended on cell genotype and was related to the expression levels of the concurrent enzyme asparagine synthetase. Bacterial subcellular distribution of L-asparaginase was also analysed along with its immunogenicity. H. pylori L-asparaginase is a novel antigen that functions as a cell-cycle inhibitor of fibroblasts and gastric cell lines. We give evidence supporting a role in the pathogenesis of H. pylori-related diseases and discuss its potential diagnostic application.     

Stroke research in GenomEUtwin.

Stroke is one of the leading causes of severe disability and death in the world. In the present article we outline possibilities and limitations for future stroke research within the GenomEUtwin. The combined sample of twins born before 1958 from Denmark, Finland, and Sweden, and available for follow-up into the second millennium for non-fatal and fatal stroke events through national inpatient and death registers exceeds 70,000 twin pairs. This sample size will enable the study of genetic influences on stroke and major stroke subtypes. Large samples of twins in GenomEUtwin have been followed up repeatedly through interviews and questionnaires concerning a variety of exposures and potential risk factors for stroke. We briefly outline how this information can be combined with the health register information for epidemiologic and genetic epidemiologic studies of stroke. We also present the number of twin pairs concordant and discordant for stroke in Denmark, Finland and Sweden, and time lags between events for twins concordant for stroke. This information illustrates that the number of affected sib pairs for linkage studies is relatively limited, but the sample sizes are promising for association studies.