Study probes how organisms evolved diverse mechanisms
Scientists have long investigated how organisms fight disease. They have also tried to mitigate the burden of disease. In a paper presented in the journal PLoS Biology, a two-man research team from the United Kingdom and the United States evaluate how Konrad et al. present an example of fungus-specific immune responses in social ants that cause the active immunisation of nest mates by infected individuals. The results provide fresh insight into our understanding of how organisms evolved diverse mechanisms that fulfil various functions, including the transfer of immunity between related individuals and the discrimination between pathogens.
Researchers from the Institute of Immunology and Infection Research at the University of Edinburgh in the United Kingdom and from Stanford University in the United States put the spotlight on Lasius neglectus ants. Once covered with lethal doses of the entomopathogenic fungus Metarhizium anisopliae, the ants were permitted to interact with their nest mates.
The nest mates were thereby exposed to fungal doses that were too low to induce a specific pattern of anti-fungal immune gene expression. According to the researchers, the recipients of the inoculum were less likely to die from a subsequent lethal dose of the same microbe. They add that the mathematical modelling suggests that these responses would enable a faster recovery for the colonies.
'As first suggested by Rosengaus and Traniello, these phenomena are strongly reminiscent of variolation as practised by humans, whereby exposure to controlled low doses of a pathogen protects individuals against future infections,' the authors write in their study.
'Unlike vaccination, however, the fungal spores transmitted in the system studied by Konrad et al. did not appear to be attenuated, for example, by digestive enzymes, and remained infective. The authors used a combination of approaches to identify the mechanisms underlying social immunisation in ant colonies: mathematical modelling; and behavioural, microbiological, immunological, and molecular techniques, which, taken together, offer an exciting proof of concept that group-level immunity may be experimentally manipulated and modelled.'
While more work needs to be performed to determine how this relates to animal and human epidemiology, the duo say it is very likely that sound evolutionary inferences may readily be made from such studies.
'It would be fruitful to examine, for instance, the cellular basis of the immune specificity suggested by gene expression patterns; whether prior exposure enables more rapid and/or stronger responses to lower doses of pathogen; how much cross-protection against other pathogens is thus generated; and whether insect social immunisation persists only as long as individuals are exposed to the pathogen or whether immune memory can produce long-term social immunisation in invertebrates. By studying social immunity at a system level in insects, perhaps we can find emergent properties that we have been missing in another important social animal — the human.'
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