Antigen-encapsulating host extracellular vesicles derived from Salmonella-infected cells stimulate pathogen-specific Th1-type responses in vivo

Salmonella Typhimurium is a causative agent of nontyphoidal salmonellosis, for which there is a lack of a clinically approved vaccine in humans. As an intracellular pathogen, Salmonella impacts many cellular pathways. However, the intercellular communication mechanism facilitated by host-derived small extracellular vesicles (EVs), such as exosomes, is an overlooked aspect of the host responses to this infection. We used a comprehensive proteome-based network analysis of exosomes derived from Salmonella-infected macrophages to identify host molecules that are trafficked via these EVs. This analysis predicted that the host-derived small EVs generated during macrophage infection stimulate macrophages and promote activation of T helper 1 (Th1) cells. We identified that exosomes generated during infection contain Salmonella proteins, including unique antigens previously shown to stimulate protective immune responses against Salmonella in murine studies. Furthermore, we showed that host EVs formed upon infection stimulate a mucosal immune response against Salmonella infection when delivered intranasally to BALB/c mice, a route of antigen administration known to initiate mucosal immunity. Specifically, the administration of these vesicles to animals stimulated the production of anti-Salmonella IgG antibodies, such as anti-OmpA antibodies. Exosomes also stimulated antigen-specific cell-mediated immunity. In particular, splenic mononuclear cells isolated from mice administered with exosomes derived from Salmonella-infected antigen-presenting cells increased CD4+ T cells secreting Th1-type cytokines in response to Salmonella antigens. These results demonstrate that small EVs, formed during infection, contribute to Th1 cell bias in the anti-Salmonella responses. Collectively, this study helps to unravel the role of host-derived small EVs as vehicles transmitting antigens to induce Th1-type immunity against Gram-negative bacteria. Understanding the EV-mediated defense mechanisms will allow the development of future approaches to combat bacterial infections.

First Report of Catenaria auxiliaris Parasitizing the Reniform Nematode Rotylenchulus reniformis on Cotton in Alabama

A new fungal parasite of the reniform nematode has been observed parasitizing nematode populations that have increased on cotton in a sandy loam field soil in the greenhouse. When enumerated, 46% of the stock reniform nematode population was colonized by this fungus. Egg, vermiform, and adult stages of the reniform nematode were observed with light microscopy and scanning electron micrography (SEM). The nematophagous fungus, Catenaria auxiliaries, was identified morphologically. There are no sequences on the GenBank to achieve a molecular identification. This nematophagous fungus has been previously reported on the beet cyst nematode in Europe (1,2); however, to our knowledge there are no reports of this fungus parasitizing the reniform nematode. In vermiform life stages of the nematode, rhizomycelium is observed in the initial phase of infection and is characterized by ovoid cells, 9.5 to 13.5 × 17.0 to 24.5 μm in diameter, separated by septa. Usually 10 to 15 ovoid cells lacking intercellular hyphal filaments are produced within each vermiform body. Rhizoids 3.5 to 4.0 μm wide develop from the rhizomycelium. Mature swollen cells produce precursor sporangia that may mature into resting spores or zoosporangia. Resting spores are yellow-to-cream, 20 to 40 μm in diameter with a reticulate appearance, and are common in the vermiform nematode life stages. Zoosporangia are ovoid, 9.5 to 13.5 × 17.0 to 24.5 μm, and will erupt from the cuticle of the vermiform nematode releasing zoospores via papillae. Zoospores are 2.9 to 4.9 μm with visible globules in the anterior region and single flagella that are 9 to 11 μm long. The zoospores swim short distances, maneuvering in the direction of the flagellum. Adult reniform females observed through SEM exhibit zoospores encysted in the metacorpus region of the nematode. Parasitized eggs are internally colonized with zoosporangia that are 20 to 25 μm in diameter. In advanced stages of infection, the eggs darken in color and zoosporangia erupt through the cuticle of the egg. Reniform nematodes visibly colonized with zoosporangia and resting spores were placed on corn meal, water, and potato dextrose agars. None of these media supported growth of the fungus, supporting our theory that this organism appears to be an obligate parasite of the nematode. Koch's postulates was completed when eggs colonized with rhizomycelium and resting spores or zoosporangia were added to cotton plants in sterile soil previously inoculated with 2,000 healthy vermiform reniform life stages. Plants were allowed to grow for 30 days in the greenhouse after which the next generation of vermiform nematodes were extracted from the soil and examined under the microscope. Rhizomycelium, resting spores, and zoosporangia were present in 42% of the reniform vermiform life stages. Morphological comparisons of the rhizomycelium, resting spores or zoosporangia, and zoospores colonizing the reniform nematodes were similar to the initial observations. Thus to our knowledge, this is the first report of Catenaria auxiliaries parasitizing the reniform nematode. References: (1) B. Kerry. J. Nematol. 12:253, 1980. (2) H. T. Tribe. Trans. Br. Mycol. Soc. 69:367, 1977.

Autoantibodies and glomerulonephritis in systemic lupus erythematosus

Autoantibody diversification to a variety of autoantigens is a hallmark for systemic autoimmunity. SLE represents a prototype. In this article the roots of the important questions probed by the Kunkel laboratory in SLE research are traced. Data from the recent animal work by the laboratory of Shu Man Fu are summarized to emphasize the importance of further exploration of autoantibody specificities in lupus with a special emphasis on nephritis and to suggest a broader perspective regarding lupus autoantibody reactivities in addition to those against nuclear components.

Discrete and discontinuous action of brown widow spider venom on the presynaptic nerve terminals of frog muscle

1. A study was made of the effects of the venom of the brown widow spider (Latrodectus geometricus) on end-plates of the frog sartorius muscle. 2. The increase in the frequency of the minature end-plate potentials (m.e.p.p.s), elicited by the venom in normal-"Ca2+" Ringer solution, occurs in discrete volleys having a sharp onset and end. The frequency of the m.e.p.p.s is high (up to 300 sec-1) and relatively constant during the volley. 3. The volleys recur at intervals during a period from 5 to 10 min after addition of the venom until the onset of electrical silence, up to 4 hr later. The activity occurs in groups containing volleys of loing and short duration. 4. Simultaneous intracellular and extracellular recording from single end-plates indicates that the volleys originate at highly localized areas of the nerve terminals. The high-frequency release of m.e.p.p.s in hypertonic sol solutions, which was studied for comparison purposes, occurs randomly over the entire end-plate. Volleys originating simultaneously at different sites are often superimposed in the intracellular recordings. 5. In high-"Ca2+" Ringer solution, the initial frequency of the m.e.p.p.s in a volley is comparatively higher. However, the frequency drops to one half its value in a few seconds. The volley then terminates or else the frequency of m.e.p.p.s remains high for some time and the volley has no sharp end. Activity occurs in groups containing both long and short volleys. Many more short (less than 5 sec) and long (greater than 30 sec) volleys occur in high-"Ca2+" solution than in normal-"Ca2+" solutions. 6. In low-"Ca2+", high-"Mg2+" Ringer solution, the volleys of m.e.p.p.s are fewer in number and much longer in duration. Intra- and extra-cellular recording of uninterruped activity during long periods suggests that in this solution the m.e.p.p.s originate diffusely rather than at discrete areas of the nerve terminals. 7. Implications of the above data on possible modes of action of the venom are discussed.