Higher stress protein levels are associated with lower humoral and cell-mediated immune responses in Pied Flycatcher females

1. The proper functioning of immune defences may be traded-off against protecting the organism from physiological stress through the induction of stress protein (HSP) synthesis. Immune function could also be negatively affected by haemoparasite infections. 2. We studied whether two induced immune responses (the humoral response to a tetanus vaccine and the T-cell-mediated response to phytohaemaglutinin (PHA) injection) were associated with the levels of two stress proteins (HSP60, HSP70), with haemoparasite infection and with condition in Pied Flycatcher, Ficedula hypoleuca Pallas, females. HSP levels, haemoparasite infection and condition were assessed on days 1 and 11 of nestling age, prior to tetanus and PHA challenges, respectively. 3. Females with higher HSP60 levels prior to tetanus challenge mounted lower humoral responses. Females parasitized by Haemoproteus showed lower humoral responses, when controlling for HSP60 levels. No association was detected for HSP70 levels. 4. Females with higher HSP60 and HSP70 levels prior to PHA challenge, independently of Haemoproteus infection, showed lower cell-mediated responses, when correcting for laying date. Female condition was not associated with immune responses. 5. These results suggest that synthesizing more HSPs to mitigate stress may be traded-off against mounting humoral and cell-mediated immune responses, and agree with immune defences being costly.