Magnitude do custo energético da ativação do sistema imune em morcegos: efeitos sazonais e da restrição alimentar
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Data
2016-10-27
Autores
Cabrera-Martinez, Lucia Velarde [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Um dos componentes da resposta imune inata é a resposta de fase aguda (RFA), a qual tem como objetivo restabelecer a homeostase e promover a cura de um organismo através de uma serie de alterações fisiológicas que podem acarretar num alto gasto energético. Algumas das alterações são aumento da taxa metabólica, temperatura corpórea (febre) e granulócitos no sangue (eosinófilos, basófilos e neutrófilos). Os animais podem também apresentar anorexia, diminuição da atividade e perda de massa corpórea, minimizando o gasto de energia durante a ativação da RFA. Em situações de aumento da demanda de energia e diminuição da ingestão calórica, os organismos estão sujeitos a uma deficiência nas reservas energéticas, a qual poderia dificultar o combate efetivo contra patógenos. Nos induzimos a ativação da RFA em morcegos frugívoros da espécie Carollia perspicillata por meio de injeção de lipopolissacarídeo (LPS). Quantificamos o custo energético da RFA e como o mesmo é afetado pela sazonalidade (inverno e verão) e disponibilidade de alimento (restrição alimentar e alimentados ad libitum). A perda de massa corpórea durante a RFA foi significativa em ambas as estações, porém apenas em morcegos em restrição alimentar, provavelmente devido a que nos morcegos em restrição alimentar foi necessária a mobilização de reservas energéticas, enquanto que morcegos alimentados ad libitum cobriram parte do custo da RFA através da mobilização de carboidratos ingeridos horas antes do experimento. Não observamos febre nem leucocitose, contudo, a razão neutrófilo/linfócito (N/L) teve aumento significativo unicamente em morcegos em restrição alimentar e durante o inverno. Este último parâmetro é também um indicador de estresse, o que sugere que à combinação de baixa disponibilidade de alimento e aumento na demanda energética para termoregulação durante o inverno pode ser uma situação estressante para estes morcegos. Aparentemente os morcegos deste grupo conseguiram ativar uma RFA, porém não foi possível mensurar se a efetividade da mesma foi comprometida. O custo energético da RFA não diferiu entre grupos experimentais. Nossos dados mostram que o custo da ativação da RFA em C. perspicillata é baixo (1% do orçamento diário de energia). Portanto, mesmo em situações onde existe maior demanda de energia e baixa disponibilidade de alimento, C. perspicillata ainda é capaz de ativar uma RFA, e consequentemente, manter a imunocompetência sem comprometer o seu orçamento de energia.
One of the innate immune response components is the APR, which can be activated by trauma, infection, stress and inflammation. The APR activation aims to restore homeostasis and health of an organism exposed to the before mentioned events, through several physiological modifications that may result in high energetic cost. Some modifications are increase in metabolic rate, fever and granulocytes in the blood (eosinophils, basophils and neutrophils). Animals may also show anorexia and body mass loss, reducing the energy expenditure during the APR activation. In situations where animals are exposed to increase energy demand and decrease caloric intake, they could experience a deficiency in energy reserves, which may hamper the effectiveness of an immune response. We induced the APR activation in the Short-tailed fruit bats (Carollia perspicillata) by LPS injection. We quantified the energetic cost of the APR and how it is affected by seasonality (winter and summer) and food availability (food restriction and fed ad libitum). Body mass loss during the APR activation was observed in both seasons, but only in bats in food restriction, probably due to the mobilization of energy reserves, while bats fed ad libitum covered part of the APR cost by the mobilization of carbohydrates from the recent ingested food. Bats did not show fever or leukocytosis, nevertheless, we found increase in N/L ratio when bats were in food restriction and during winter. This parameter is also a stress indicator, so probably the combination of limited food availability and increase in the energy demand for thermoregulation during winter, may be a stressful situation for this bat. It seems that bats from this group were able to activate the APR, nevertheless we could not measure if the effectiveness of the response was jeopardized. The energetic cost of the APR activation did not vary between experimental groups. Our results showed that for C. perspicillata, activating the APR entails low energy cost (1% of the daily energy budget). Thus, they seem to be capable of activating an immune response even in situations that demand more energy and when food availability is limited, and consequently preserve immunocompetence without compromising their energy budget.
One of the innate immune response components is the APR, which can be activated by trauma, infection, stress and inflammation. The APR activation aims to restore homeostasis and health of an organism exposed to the before mentioned events, through several physiological modifications that may result in high energetic cost. Some modifications are increase in metabolic rate, fever and granulocytes in the blood (eosinophils, basophils and neutrophils). Animals may also show anorexia and body mass loss, reducing the energy expenditure during the APR activation. In situations where animals are exposed to increase energy demand and decrease caloric intake, they could experience a deficiency in energy reserves, which may hamper the effectiveness of an immune response. We induced the APR activation in the Short-tailed fruit bats (Carollia perspicillata) by LPS injection. We quantified the energetic cost of the APR and how it is affected by seasonality (winter and summer) and food availability (food restriction and fed ad libitum). Body mass loss during the APR activation was observed in both seasons, but only in bats in food restriction, probably due to the mobilization of energy reserves, while bats fed ad libitum covered part of the APR cost by the mobilization of carbohydrates from the recent ingested food. Bats did not show fever or leukocytosis, nevertheless, we found increase in N/L ratio when bats were in food restriction and during winter. This parameter is also a stress indicator, so probably the combination of limited food availability and increase in the energy demand for thermoregulation during winter, may be a stressful situation for this bat. It seems that bats from this group were able to activate the APR, nevertheless we could not measure if the effectiveness of the response was jeopardized. The energetic cost of the APR activation did not vary between experimental groups. Our results showed that for C. perspicillata, activating the APR entails low energy cost (1% of the daily energy budget). Thus, they seem to be capable of activating an immune response even in situations that demand more energy and when food availability is limited, and consequently preserve immunocompetence without compromising their energy budget.
Descrição
Palavras-chave
Custo energético, Resposta de fase aguda, Taxa Metabólica, Sazonalidade, Restrição alimentar, Energetic cost, Immune response, Metabolic rate, Seasonality, Food restriction, Acute phase response