Trade-offs within the immune systems of female White-footed Mice, Peromyscus leucopus

1. In many vertebrates, immune activity is compromised when other expensive activities are concurrent. One explanation for such patterns includes trade-offs between immune activity and other expensive physiological processes. Trade-offs among different immune responses themselves may also occur, but thus far few data exist to substantiate them. 2. We predicted that immune activity in female White-footed Mice, Peromyscus leucopus, would be weak (relative to sham-treated controls) if another immune response was already ongoing. To test this hypothesis, we examined (i) the effects of inflicting a cutaneous wound on cell-mediated immune activity one day after wounding, and (ii) the effects of inducing cell-mediated immune activity on the cutaneous wound-healing process when wounds were inflicted one day after the immune challenge. 3. Prior wounding dampened cell-mediated immune responses and induction of cellmediated immune activity altered progression of wound healing. Immune challenges did not affect reproductive tissue masses, however, as has been detected in males of this species. Also, concentrations of circulating glucocorticoids, which are known modulators of immune activity, were not dramatically different between treatment and sham groups. 4. In sum, our results provide evidence that some immune responses can negatively influence other recent immunological activity. Further study is warranted, however, to pinpoint the molecular mechanisms underlying these apparent trade-offs and determine whether induction of immune activity may sometimes prime instead of hinder subsequent immune responses.