The old adage goes that there is nothing new under the sun. But some may be surprised to find that humans aren’t the only creatures to have invented vaccines. A study just published in the Journal of Experimental Biology by Gyan Harwood of the University of Illinois, Urbana-Champaign, confirms that honey bees got there before us. It also suggests that these carry out operations similar to childhood vaccination-type programs prime-boost (ie “double vaccination”, in which the first activates the immune response, the second strengthens it).
Being gregarious, honey bees are constantly at risk of disease spreading in their hives. Most animals living in crowded conditions possess a robust immune system. For this reason, entomologists have long wondered why the same does not happen to honey bees, which actually have fewer genes that modulate the immune system than most solitary bees.
The antigen of the queen bee
Part of the answer, which emerged in 2015, is that queen bees vaccinate their eggs by transferring protein fragments from disease-causing pathogens into them before they are laid.
These proteins act as antigens that trigger the development of a protective immune response in developing specimens. But this observation has led to the question of how the queen receives her supply of antigens to begin with, since she only feeds on royal jelly, a substance produced by worker bees in a phase of their life (prior to the period). which they spend flying freely to get nectar and pollen) in which they feed the larvae. Dr Harwood then wondered whether these nurse bees incorporate, in the royal jelly they produce, fragments of the pathogens contained in the supplies brought into the hive by the bees who came out to get food.
To put his idea to the test, he teamed up with a group from the University of Helsinki, Finland, led by Heli Salmela. Together they collected about 150 nurse bees, dividing them into six mini hives without queen bee, in which there were broods of larvae to look after. Instead of nectar, they gave the nurse bees water and sugar, and in three of these hives they “corrected” this syrup with Paenibacillus larvae, a bacillus that causes a deadly disease in hives called American foulbrood.
In this case, to avoid such an infection, Dr. Harwood and Dr. Salmela previously subjected the pathogens to heat, killing them. They also applied a fluorescent dye to the dead bacteria to make it easier to trace their subsequent fates. And, of course, the fluorescent microscopes confirmed that fragments of Paenibacillus larvae they entered the royal jelly, produced by those bees that had been fed with “correct” water and sugar. Additionally, examination of this royal jelly revealed elevated levels – compared to that from bees that had not been fed Paenibacillus larvae – of an antimicrobial peptide known as defensin-1. This substance is believed to help the immune systems keep bacterial infections at bay.
Taken together, these findings suggest that nurse bees actually pass antigens to the queen bee via their royal jelly, which then inoculates them into its eggs. This also means – since the larvae also receive royal jelly in the first few days after hatching – that the nurse bees also inoculate the larvae.
Each newborn bee is therefore vaccinated twice. Whether this is simply an approach remains to be seen belt-and-braces (of a double precaution), or is actually the equivalent of vaccination prime-boost for humans, where the second vaccination multiplies the effects of the first. But whatever the truth, it appears to offer protection. Not so much herd immunity as swarm immunity.
(Translation by Federico Ferrone)
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