Role of macrophages in protecting honey bees Apis mellifera (Hymenoptera: Apidae) against the pathogen Paenibacillus larvae infection

Abstract

The American full brood disease severely affects the health of bees, which leads to significant economic losses in the beekeeping industry. Spores of Paenibacillus larvae are the causative agent of the disease that mainly affects young bee larvae. Some Researches indicated that adult bees can tolerate a high load of these spores without showing any pathological symptoms. Is there a role for the immunity system in protecting them from infectious disease? Have honey bees Apis mellifera L. ) Hymenoptera: Apidae) can develop additional strategies in their defense mechanism allow them to use the Macrophages for protection at the level of humoral immunity. Therefore, this study focuses on clarifying an aspect of immunity that helps enhance this defensive role. So, honey bee colonies were given Paenibacillus spores as part of their feeding routine. After fifty days, worker nurse bees were randomly selected from both treated and non-treated bee colonies. The ventriculus and the small intestine were dissected and prepared for examination using a Transmission Electron Microscope (TEM). This study proved that the existence of 5 types of Macrophages that have been either free in the interstitial fluid or stable in the intestinal tissue. These types of Macrophages are different in their structures and external appearance. One type of them contains sensory organelles such as Toll-like Receptors (TLDs) and Pattern Recognition Receptors (PRRs). Others have different methods used for obtaining the bacterial nutrients and have different structural systems that match their way of digesting food ranging from simple to advance. As well as they have an execratory apparatus that corresponds to their internal structure and digestion methods.