Protein nutrition governs within-host race of honey bee pathogens.

Multiple infections are common in honey bees, Apis mellifera, but the possible role of nutrition in this regard is poorly understood. Microsporidian infections, which are promoted by protein-fed, can negatively correlate with virus infections, but the role of protein nutrition for the microsporidian-virus interface is unknown. Here, we challenged naturally deformed wing virus - B (DWV-B) infected adult honey bee workers fed with or without pollen ( = protein) in hoarding cages, with the microsporidian Nosema ceranae. Bee mortality was recorded for 14 days and N. ceranae spore loads and DWV-B titers were quantified. Amongst the groups inoculated with N. ceranae, more spores were counted in protein-fed bees. However, N. ceranae infected bees without protein-diet had reduced longevity compared to all other groups. N. ceranae infection had no effect on protein-fed bee's longevity, whereas bees supplied only with sugar-water showed reduced survival. Our data also support that protein-feeding can have a significant negative impact on virus infections in insects. The negative correlation between N. ceranae spore loads and DWV-B titers was stronger expressed in protein-fed hosts. Proteins not only enhance survival of infected hosts, but also significantly shape the microsporidian-virus interface, probably due to increased spore production and enhanced host immunity.

Parasites suppress immune-enhancing effect of methionine in nestling great tits.

After birth, an organism needs to invest both in somatic growth and in the development of efficient immune functions to counter the effects of pathogens, and hence an investment trade-off is predicted. To explore this trade-off, we simultaneously exposed nestling great tits (Parus major) to a common ectoparasite, while stimulating immune function. Using a 2 × 2 experimental design, we first infested half of the nests with hen fleas (Ceratophyllus gallinae) on day 3 post-hatch and later, on day 9-13 post-hatch, and then supplemented half of the nestlings within each nest with an immuno-enhancing amino acid (methionine). We then assessed the non-specific immune response by measuring both the inflammatory response to a lipopolysaccharide (LPS) and assessing the levels of acute phase proteins (APP). In parasite-infested nestlings, methionine had a negative effect on body mass close to fledging. Methionine had an immune-enhancing effect in the absence of ectoparasites only. The inflammatory response to LPS was significantly lower in nestlings infested with fleas and was also lower in nestlings supplemented with methionine. These patterns of immune responses suggest an immunosuppressive effect of ectoparasites that could neutralise the immune-enhancing effect of methionine. Our study thus suggests that the trade-off between investment in life history traits and immune function is only partly dependent on available resources, but shows that parasites may influence this trade-off in a more complex way, by also inhibiting important physiological functions.

Enhancement of respiratory immunity to Pasteurella multocida by cholera toxin in rabbits.

Cholera toxin (CT) is a potent adjuvant for the mucosal immune system. The purpose of this study was to determine if coadministration of CT with a potassium thiocyanate extract of Pasteurella multocida (PTE) leads to enhanced anti-PTE antibody activity and increased protection of rabbits against infection with P. multocida and associated disease. Groups of rabbits were immunized intranasally on days 0, 7, and 14, with phosphate buffered saline (PBS), 200 micrograms of CT, 1.0 mg of PTE, or 1.0 mg PTE with 200 micrograms CT. Nasal lavage and serum samples were collected over 28 days after initial immunization and evaluated by ELISA for specific antibody directed against PTE. Marked increases in serum (IgG) and nasal lavage (IgA) anti-PTE antibody activity were found beginning after day 14 in rabbits immunized with PTE. Rabbits immunized with PTE and CT demonstrated further increases in this activity. Tracheobronchial lavage samples collected at the time of necropsy demonstrated a significant level of anti-PTE IgA activity in animals immunized with PTE, and coadministration with CT stimulated a further significant increase in this activity. Groups of similarly immunized rabbits were challenged 16 days after initial immunization with 5 x 10(7) CFUs of P. multocida. Nasal lavage samples were cultured for P. multocida over the next 10 days. Rabbits were euthanized within 10 days after challenge, tissues cultured for P. multocida, and histopathologic lesion severity graded using a numeric scale. Rabbits immunized with PTE survived longer, had less severe lesions of the lungs, pleura, and liver, and fewer P. multocida CFUs cultured from samples than PBS or CT controls. Coadministration of CT led to further reductions in lesion severity of those tissues and numbers of P. multocida CFUs cultured from samples. Increased nasal turbinate atrophy of rabbits immunized with PTE with or without CT was associated with increased mean survival time. In summary, coadministration of CT with PTE enhanced protective immunity to P. multocida disease and infection in rabbits.