Phytohemagglutinin‐induced skin swelling in birds: histological support for a classic immunoecological technique

Abstract

Summary 1.Measurements of phytohemagglutinin (PHA)-induced tissue swelling are arguably the most popular surrogates for immunocompetence in wild birds. It is largely unresolved, however, whether the basic assumption underlying these measures is valid, particularly whether more swelling represents a 'better' or 'stronger' cell-mediated immune response. 2. In this study we took a first step towards such validation by characterizing immune cell infiltration over time into the wing-webs (patagia) of PHA-challenged House Sparrows ( Passer domesticus ). Relative to saline-injected wing-webs, PHA-injected wingwebs displayed intensive infiltration of many immune cell types, including basophils, eosinophils, heterophils, lymphocytes, macrophages and thrombocytes. The abundance of most of these cell types changed over the course of the swelling response (6 -48 h postinjection). Peak infiltration time varied depending on cell type. At several time points, significant correlations between the numbers of some cell types (particularly heterophils) and the degree of swelling were detected. 3. Together, these data indicate that PHA-induced swelling is related to heightened immune cell activity in House Sparrows, but also that the PHA swelling response in this species is dynamic and involves both innate and adaptive components of the immune system. We thus caution against interpreting larger swellings as 'greater cell-mediated immunocompetence', given the complex nature of this immune response.

Mothers adjust offspring sex to match the quality of the rearing environment

“…Because relative 'condition' is a complex measure, the indices used here may not have accurately or completely measured changes in condition to nutritional stress. However, these morphological and physiological measures have typically been associated with condition, health and survival in a number of bird species [39,41,44], including the closely related Gouldian finch (Erythrura gouldiae) [36,42], and even in their own offspring (this study). Interestingly, in contrast to other Erythrura finches (i.e.…”

“…PHA is a lectin that stimulates innate and adaptive immune responses, including those giving rise to a measurable inflammatory response [44]. Each bird's right and left wing webs were injected with either PHA or sterile phosphate-buffered saline (PBS), respectively [45,46] and the consequent swellings measured with pressure-sensitive digital callipers (0.01 mm) 24 h later.…”

A trade-off between embryonic development rate and immune function of avian offspring is revealed by considering embryonic temperature

“…The inflammatory response at the point of injection was measured after 24 h with a pressure-sensitive micrometer to the nearest 0.01 mm [5]. This inflammatory response reflects an induced innate and adaptive immune response [11,14]. We also measured the activity of natural antibodies that circulate in normal individuals in the absence of exogenous antigenic stimulation as a measure of constitutive innate immune defences [14].…”

“…We used two common assays of immune function [5,11,12] that have been related to offspring survival and disease resistance (e.g. [13]).…”

The effects of neonatal handling on adrenocortical responsiveness, morphological development and corticosterone binding globulin in nestling American kestrels (Falco sparverius)

“…Butler and Dufty [12] demonstrated that 15 min of daily handling of nestling American kestrels and European starlings (Sturnus vulgaris) had no effect on the amount of swelling induced by the mitogen phytohemagglutinin (PHA). PHA, which has been thought to reflect the robustness of cell-mediated immunity, may instead stimulate a complex response involving multiple components of the immune system [42,62]. Thus, handling nestlings does not appear to affect immunoresponsiveness.…”