Murray State University

Poster Title

Energy Costs and Trade-Offs of the Adaptive Immune System in Old-Field Mice (Peromyscus polionotus)

Institution

Murray State University

Abstract

A high energetic cost of adaptive immune defenses is assumed in theoretical discussions of immune responses in animals. Little quantitative data are available to test the assumption, however, especially for mammalian species. We tested the null hypotheses that 1) there is no difference between energy expenditure of challenged and static cell-mediated and humoral immune systems and 2) there is no change in the magnitude of a humoral immune response when a cell-mediated immune response is introduced. To test these hypotheses, we used a two-by-two experimental design with humoral (sheep red blood cells) and cell-mediated (2,4- dinitrofluorobenzene) challenges as the independent variables. Using adult male old-field mice (Peromyscus polionotus), we measured hemagglutination, inflammation, metabolic rates, and organ masses to assess the energetic cost and potential energy trade-offs associated with cellmediated and humoral immunity, and interactions between them. We rejected our first hypothesis. The cell-mediated, but not the humoral immune response, was associated with a 13.7% increase in resting metabolic rate, while neither response was associated with a significant change in daily metabolic rate. Also, the cell-mediated response was associated with a significant decrease in testes mass and colon length. Reduced organ sizes may indicate that part of the cost of mounting a cell-mediated response was met through reduced energy allocation to the digestive and reproductive systems. The cell-mediated response had no measurable effect on the humoral response. Our results supported the assumption of a significant energetic cost of cell-mediated, but not humoral immune defense.

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Energy Costs and Trade-Offs of the Adaptive Immune System in Old-Field Mice (Peromyscus polionotus)

A high energetic cost of adaptive immune defenses is assumed in theoretical discussions of immune responses in animals. Little quantitative data are available to test the assumption, however, especially for mammalian species. We tested the null hypotheses that 1) there is no difference between energy expenditure of challenged and static cell-mediated and humoral immune systems and 2) there is no change in the magnitude of a humoral immune response when a cell-mediated immune response is introduced. To test these hypotheses, we used a two-by-two experimental design with humoral (sheep red blood cells) and cell-mediated (2,4- dinitrofluorobenzene) challenges as the independent variables. Using adult male old-field mice (Peromyscus polionotus), we measured hemagglutination, inflammation, metabolic rates, and organ masses to assess the energetic cost and potential energy trade-offs associated with cellmediated and humoral immunity, and interactions between them. We rejected our first hypothesis. The cell-mediated, but not the humoral immune response, was associated with a 13.7% increase in resting metabolic rate, while neither response was associated with a significant change in daily metabolic rate. Also, the cell-mediated response was associated with a significant decrease in testes mass and colon length. Reduced organ sizes may indicate that part of the cost of mounting a cell-mediated response was met through reduced energy allocation to the digestive and reproductive systems. The cell-mediated response had no measurable effect on the humoral response. Our results supported the assumption of a significant energetic cost of cell-mediated, but not humoral immune defense.