Honeybee apisimin and plant arabinogalactans in honey costimulate monocytes

Here we determined whether immunostimulatory plant-derived arabinogalactan proteins (AGPs) and the honeybee-derived protein apisimin are present in varieties of New Zealand honey. Apisimin is a protein of unknown function secreted from the glands of honeybees into Royal Jelly, forming a complex with apalbumin1 capable of stimulating lymphocyte proliferation. AGPs were abundant in kanuka honey with lesser amounts in manuka, kowhai and clover honeys, but absent from Royal Jelly. Apisimin was present in all honeys, as well as Royal Jelly. We report that apisimin shares with honey AGPs the ability to stimulate the release of TNF-α from blood monocytes. Further, it synergizes with AGPs to enhance the release of TNF-α, via a mechanism not involving the formation of a complex with AGPs. In summary, this study provides evidence that AGPs and apisimin are commonly present in different floral varieties of honey, and hence contribute to their immunostimulatory properties.