Is Immunity Energetically Costly?

The immune system is critical to survival and subsequent reproductive success of organisms. Many researchers have suggested that some components of the immune system, especially adaptive immunity, are energetically expensive. Our goal was to quantify the cost of the immune system to determine whether trade-offs in energy use occur between branches of the immune system and between the immune system and other physiological processes during an immune response. We tested the null hypothesis that an ongoing humoral immune response has no effect on the development of a cell-mediated immune response. Using adult male old-field mice, Peromyscus polionotus, cell-mediated responses were induced in cell-mediated/humoral (CH; n=10) and cell-mediated (Cm; n=10) adult male mice using dinitrofluorobenzene. A humoral response was induced using sheep red blood cells. Results were compared with a control group (Ct; n=10). We measured the energetic cost and strength of the immune responses through analysis of daily metabolic rate, resting metabolic rate, red and white blood cell counts, pinnae measurements, and hemagglutination assays. Metabolic rates of the CH and Cm mice did not differ significantly from those of Ct mice, despite significantly smaller masses of immune and vital organs in the latter group. There was an unexpected significant increase of innate activity in the CH mice as compared to the Ct mice. In addition, we failed to find any significant difference between the Cm and CH groups in any measured parameter. Thus, our work showed no significant trade-offs between the humoral and cell-mediated immune systems or between the adaptive and innate immune systems. Importantly, our results also did not support the widelyused assumption of a high energetic cost of adaptive immunity