The immune response of bats differs between pre-migration and migration seasons

Abstract

Maintaining a competent immune system is energetically costly and thus immunity may be traded against other costly traits such as seasonal migration. Here, we tested in long-distance migratory Nathusius’ pipistrelles (Pipistrellus nathusii), if selected branches of immunity are expressed differently in response to the energy demands and oxidative stress of aerial migration. During the migration period, we observed higher baseline lymphocyte and lower neutrophil levels than during the pre-migration period, but no stronger response of cellular effectors to an antigen challenge. Baseline plasma haptoglobin, as a component of the humoral innate immunity, remained similar during both seasons, yet baseline plasma haptoglobin levels increased by a factor of 7.8 in migratory bats during an immune challenge, whereas they did not change during the pre-migration period. Oxidative stress was higher during migration than during pre-migration, yet there was no association between blood oxidative status and immune parameters, and immune challenge did not trigger any changes in oxidative stress, irrespective of season. Our findings suggest that humoral effectors of the acute phase response may play a stronger role in the first-line defense against infections for migrating bats compared to non-migrating bats. We conclude that Nathusius’ pipistrelles allocate resources differently into the branches of their immune system, most likely following current demands resulting from tight energy budgets during migration.

Is a Little Enough? Paucity of Immune Proteins in Serum of Precocial Neonates of a Marine Carnivoran—the Atlantic Grey Seal

“…As already said, we saw no evidence of an acute phase response in any of our subjects indicated by a dramatic increase in innate immunity proteins. Although we are unwilling to do so on our wild seal pups, responses to an infection stimulus in neonates could be tested by administering an infective dose of a bacterium or a virus, or simple pyrogens such as bacterial lipopolysaccharide (LPS), whereupon dramatic increases in all acute phase proteins should occur, as has been done in other species (Voigt et al, 2020). A better way would be to sample animals undergoing natural infections.…”

Learning from Bats to Escape from Potent or Severe Viral Infections

“…The immune challenge among bats does not alter their oxidative stress irrespective of their pre-migration and migration seasons [38]. However, bats have higher baseline leukocytes but lower neutrophil numbers during their migratory seasons as compared to their pre-migratory season.…”

“…However, bats have higher baseline leukocytes but lower neutrophil numbers during their migratory seasons as compared to their pre-migratory season. Their plasma haptoglobin (a humoral innate immune component) levels also remain same during both seasons [38]. However, plasma haptoglobin level of migratory bats increases upon an immune (LPS) challenge that remains unchanged in non-migratory or pre-migratory bats under the same immunogenic stimulation.…”

“…For example, relapse at the beginning of the migration may reduce the prevalence of highly virulent or infectious viruses by amplifying death of infected hosts during migration, especially for highly transmissible viruses and those transmitted during migration or breeding season. The long-distance migratory Nathusius' pipistrelles (Pipistrellus nathusii) show difference in the immune status, for example, during migration they have increased number of lymphocytes with decreased neutrophils as compared to the non or pre-migratory period [38]. The oxidative stress is higher during migration period without any association between blood oxidative status and immunological impact.…”

Body size affects immune cell proportions in birds and non-volant mammals, but not bats

“…If larger fliers are not as efficient at circulating protective cells throughout their bodies, then they might require greater quantities of cells (Ruhs et al, 2020 preprint). It should be noted that the high energetic costs of flight have varying impacts on the immune system (Hasselquist et al, 2007;Voigt et al, 2020;Nebel et al, 2012). While birds and bats have much in common in terms of constraints that accommodate the ability to fly, the evolution of flight likely impacted the dynamics between body size, physiological traits and the exposure risk to pathogens relative to that of non-volant birds and mammals.…”