A striking example of immunosenescence is seen in the honey bee (Apis mellifera) worker caste. The bees' age-associated transition from hive duties to more risky foraging activities is linked to a dramatic decline in immunity. Explicitly, it has been shown that an increase in the juvenile hormone (JH) level, which accompanies onset of foraging behavior, induces extensive hemocyte death through nuclear pycnosis. Here, we demonstrate that foragers that are forced to revert to hive-tasks show reversal of immunosenescence, i.e. a recovery of immunity with age. This recovery, which is triggered by a social manipulation, is accompanied by a drop in the endogenous JH titer and an increase in the hemolymph vitellogenin level. Vitellogenin is a zinc binding glycolipoprotein that has been implicated in the regulation of honey bee immune integrity. We also establish that worker immunosenescence is mediated by apoptosis, corroborating that reversal of immunosenescence emerges through proliferation of new cells. The results presented here, consequently, reveal a unique flexibility in honey bee immunity-a regulatory plasticity that may be of general biological interest.

Accumulation of oxidative stress-induced damage in brain tissue plays an important role in the pathogenesis of normal aging and neurodegenerative diseases. Neuronal oxidative damage typically increases with age in humans, and also in the invertebrate and vertebrate model species most commonly used in aging research. By use of quantitative immunohistochemistry and Western blot, we show that this aspect of brain senescence is largely decoupled from chronological age in the honey bee (Apis mellifera). The bee is a eusocial insect characterized by the presence of a reproductive queen caste and a caste of functionally sterile female workers that performs various alloparental tasks such as nursing and foraging. We studied patterns of oxidative nitration and carbonylation damage in the brain of worker bees that performed nurse tasks as 8-and 200-day-olds and foraging tasks as 20-and 200-day-olds. In addition, we examined 180-day-old diutinus bees, a stress-resistant temporal worker form that survives unfavorable periods. Our results indicate that nitration damage occurs only at low levels in vivo, but that a 60-kDa protein from honey bee brain is selectively nitrated by peroxynitrite in vitro. Oxidative carbonylation is present at varying levels in the visual and chemosensory neuropiles of worker bees, and this inter-individual variation is better explained by social role than by chronological age.

Vitellogenin is a yolk precursor protein in most oviparous females. In the advanced eusocial honeybee, Apis mellifera (Hymenoptera: Apidae), vitellogenin has recently attracted much interest as this protein, in addition to a classical function in oocyte development in the reproductive queen caste, has evolved functions in the facultatively sterile female worker caste not documented in other species. However, research on the spatial dynamics of vitellogenin in various tissues is not easily performed with available tools. Here we present an immunogold staining procedure that visualizes honeybee vitellogenin in resin embedded tissue. To establish the protocol, we used ovaries of worker bees from colonies with and without a queen. Under the first condition, vitellogenin is assumed not to be present in the workers' ovaries. Under the second condition, the ovaries of worker bees become vitellogenic, with abundant opportunities for detection of complex patterns of vitellogenin uptake and storage. By use of this experimental setup, the staining method is shown to be both sensitive and specific. To demonstrate the functional significance of the protocol, it was subsequently used to identify vitellogenin protein in the hypopharyngeal glands (brood food producing head glands) of nursing worker bees and in adjacent head fat body cells for the first time. Localization of vitellogenin in these tissues supports previously hypothesized roles of vitellogenin in social behavior. This protocol thus provides deeper insights into the functions of vitellogenin in the honeybee.

In a global transcriptome analysis of three natural and three manipulated honeybee worker phenotypes at different ages, we have investigated the distribution of investment in somatic maintenance of the fat body. Gene expression is modulated so that the bees are able to resist the most life-threatening challenges at the actual life stage. Different modes of maintenance and repair are regulated, apparently to meet the environmental challenges most detrimental to survival and reproductive potential for the hive. We observed a broad down-regulation of genomic and cellular maintenance in the short-lived foragers and nurse bees compared to the long-lived winter bees. Our results show that survival and reproduction of the entire hive is given priority over the individual bees, hence supporting the idea of the honeybee society as a superorganism. Our results also fit the disposable soma theory of aging.