AN OLD SAW has it that there is nothing new under the sun. But it may still come as a surprise that human beings are not alone in having invented vaccination. Work just published in the Journal of Experimental Biology by Gyan Harwood of the University of Illinois, Urbana-Champaign, confirms that honeybees got there first. It also suggests that they run what look like the equivalent of prime-boost childhood vaccination programmes.
Being gregarious, honeybees are at constant risk of diseases sweeping through their hives. Most animals which live in crowded conditions have particularly robust immune systems, so it long puzzled entomologists that honeybees do not. Indeed, they actually possess fewer immune-related genes than most solitary bees.
Part of the answer, discovered in 2015, is that queen bees vaccinate their eggs by transferring into them, before they are laid, fragments of proteins from disease-causing pathogens. These act as antigens which trigger the development of a protective immune response in the developing young. But that observation raises the question of how the queen receives her antigen supply in the first place, for she subsists purely on royal jelly, a substance secreted by worker bees which are at the stage of their lives (which precedes the period that they spend flying around foraging for nectar and pollen) when they act as nurses to larvae. Dr Harwood therefore wondered if the nurses were incorporating into the royal jelly they were producing, fragments from pathogens they had consumed while eating the victuals brought to the hive by the foragers.
To test this idea, he teamed up with a group at the University of Helsinki, in Finland, led by Heli Salmela. Together, they collected about 150 nurse bees and divided them among six queenless mini hives equipped with broods of larvae to look after. Instead of nectar, they fed the nurses on sugar-water, and for three of the hives they laced this syrup with Paenibacillus larvae, a bacterium that causes a hive-killing disease called American foulbrood.
In this case, to stop such an infection happening, Dr Harwood and Dr Salmela heat-treated, and so killed, the pathogens in advance. They also labelled the dead bacteria with a fluorescent dye, to make their subsequent fates easy to track. And, sure enough, fluorescent microscopy confirmed that fragments of P. larvae were getting into royal jelly secreted by those bees which had been fed with the laced sugar-water. Moreover, examination of this royal jelly revealed elevated levels, compared with royal jelly from bees that had not been dosed with P. larvae, of an antimicrobial peptide known as defensin-1. This substance is thought to help bee immune systems fend off bacterial infections.
All told, these findings suggest that nurse bees are indeed, via their royal jelly, passing antigens on to the queen for inoculation into her eggs. They also mean, because larvae, too, receive royal jelly for the first few days after they hatch, that the nurses are inoculating their larval charges as well. Each infant bee is therefore being vaccinated twice.
Whether this is simply a belt-and-braces approach, or is actually the equivalent of a prime-boost human vaccination in which the second dose multiplies the effect of the first, remains to be determined. But either way, it seems protective. Not so much herd, as swarm, immunity.■
This article appeared in the Science & technology section of the print edition under the headline “Swarm immunity”