ABSTRACT
The ability to adhere to and spread on a surface is a common property of insect blood cells. Spreading on a glass surface by insect hemocytes is often used as a measure of immune fitness that can be inhibited by some insect pathogens and parasites. Here, we report that upon infection of the tobacco hornworm Manduca sexta with either a fungus (Beauveria bassiana) or a bacterium (Photorhabdus luminescens), a new type of hemocyte, not previously observed in healthy insects, was found in hemocyte monolayers. These cells have a distinctive morphology, characterised by extreme spreading ability. They achieve a diameter of up to 120 microm after 1 h on glass coverslips and are therefore extremely thin. These hyper-spreading cells first appear in fungal-infected insects prior to hyphal growth. Their numbers later fall to zero as the pathogen begins to proliferate. The same hyper-spreading cells are induced after a 24 h delay following an injection of laminarin, a source of the fungal cell wall polymer beta-1,3-glucans. Wounding, on the other hand, did not cause the appearance of hyper-spreading cells. Evidence is presented here that is consistent with these spreading cells having a role in the cellular immune response of nodule formation.
Subject(s)
Cell Adhesion/drug effects , Cell Size/drug effects , Hemocytes/cytology , Hemolymph/cytology , Manduca/cytology , Animals , Cell Adhesion/immunology , Cell Aggregation/drug effects , Cell Aggregation/immunology , Cell Size/immunology , Glucans , Hemocytes/immunology , Hemocytes/microbiology , Hemolymph/immunology , Hemolymph/microbiology , Manduca/immunology , Manduca/microbiology , Microscopy, Confocal , Microscopy, Electron, Scanning , Mitosporic Fungi/metabolism , Photorhabdus/metabolism , Polysaccharides/pharmacologyABSTRACT
The desert locust Schistocerca gregaria contains a relatively simple but abundant gut microbiota which originated from the insect's diet. The gut bacterial population is dominated by Enterobacteriaceae with a major component of enterococci. Microbial metabolism of secondary plant chemicals in the locust gut produces phenolics useful to the locust host. Some products are antimicrobial and contribute to host defense against pathogens, others are employed by the host as components of the aggregation pheromone. This dual benefit suggests a closer degree of integration between the locust and its microbial community than was previously suspected.
