Funded by:
HHMI and the Committee
on Institutional Studies and Research, MSU
Energy assimilated = kJ ingested - kJ excreted - kJ egested -
kJ Basal Metabolism
- kJ Locomotion - kJ Reproduction - kJ Immunity?
Question
1: Should energy expenditure for immune functions be incorporated
into energy budget equations?
My students and I are testing two primary null hypotheses:
Is there a significant energetic cost associated
with maintaining
an immune system?
Adult male white-footed mice Peromyscus leucopus) were given injections of Cyclophosphamide (CY), an immunosuppressant, or saline every other day. The resting (RMR) and daily (DMR) metabolic rates were periodically measured. White blood cell counts (WBC) were made at the beginning and end of the experiment. The animals were dissected and the wet and dry masses of organs measured. |
Stephen Compton prepares the metabolic chamber for
measurement of the oxygen consumption of a white-footed mouse.
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Lee Webb collects blood by heart puncture for measurement of blood parameters. |
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Stephen injects an animal with Cyclophosphamide.
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There were no significant differences in the resting metabolic
rates of animals whose immune system was suppressed (CY) compared
with those whose immunity was normal (control). There were
also no significant differences in the masses of the intestinal,
vital, or reproductive organs. |
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There was no significant difference in daily rates of
energy use by animals whose immune system had been suppressed compared
with those whose immune system was not compressed. |
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CONCLUSION:
There was no significant cost associated with maintaining the immune
system. Further study is needed, however, using more complete
immunosuppression.
Question 2: Is there a significant
energy cost of mounting an
immune response?
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Adult male white-footed mice were injected with sheep red blood cells (SRBC) at the beginning of the experiment to challenge the humoral branch of the immune system. Near the end of the experiment the animals were injected with phytohemagglutinen (PHA) to challenge the cell-mediated branch of the immune system. Resting and daily metabolic rates were measured periodically throughout the experiment. Animals were dissected and the wet and dry masses of the vital, intestinal, and reproductive organs were measured. |
Stephen and Lee trap for white-footed mice. |
Animals
were dissected and the reproductive organs removed.
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Stephen and Dr. Derting get the oxygen analyzer running again. |
Injections of SRBC and PHA resulted in a significant increase
in WBCs. There was no significant increase in resting or
daily metabolic rates, however. Thus, animals did not accommodate
the cost of mounting a mild immune response through increases
in energy ingestion. |
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Energy allocation to the small intestine and the testes
was significantly less in the immuno-challenged males. Thus,
trade-offs in energy allocation between the immune system and
the reproductive and digestive systems may fuel the cost of mounting
an immune response. |
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