Health impact of phytohaemagglutinin-induced immune challenge on great tit (Parus major) nestlings

Abstract

Assuming that immune function is resource-limited, it can be expected to compete with other important functions of an organism for the total resource pool, giving rise to trade-offs in resource allocation. To test whether such a trade-off exists between immune defence and growth, the physiological impact of an immune challenge was examined in great tit (Parus major) nestlings, using phytohaemagglutinin (PHA) as a novel antigen. Nestlings injected intradermally with PHA in wing webs at 8 days of age produced a heterophilic response, while their growth was not suppressed in comparison with untreated control siblings. Nestlings that grew poorly produced a weaker cutaneous response to PHA inoculation than well-growing nestlings. These two results suggest that the response to PHA (a measure of the intensity of T-lymphocyte mediated immune responsiveness) is resource demanding, but these resources are not reallocated from those used for growth. This finding can be reconciled with current hypotheses, which propose that the currency in trade-offs between immune response and other demands on the organism is not necessarily energy or macronutrients but may instead be based on immunopathology, carotenoids, or production of free radicals.