The PHA Test as an Indicator of Phagocytic Activity in a Passerine Bird

Abstract

Several techniques in ecological immunology have been used to assess bird immunocompetence thus providing useful information to understand the contribution of the immunological system in life-history decisions. The phytohaemagglutinin (PHA)-skin test has been the most widely employed technique being interpreted as the sole result of T lymphocytes proliferation and hence used to evaluate acquired immunological capacity. However, the presence of high numbers of phagocytic cells in the swelling point has cast some doubt about such an assumption. To address this issue, we collected blood from 14 days-old nestlings of spotless starling (Sturnus unicolor), administered subcutaneous PHA immediately after and then measured the swelling response 24 hours later. Differential counts of white blood cells suggested that an intense development of acquired immunological defences was taking place. The phagocytic activity of both heterophiles and monocytes was also very intense as it was the swelling response. Moreover, our results show, for the first time in birds, a positive relationship between the phagocytic activity of both kinds of cells and the swelling response. This broadens the significance of the PHA test from reflecting T lymphocytes proliferation -as previously proposed but still undetermined in vivo- to evaluate phagocytosis as well. In other words, our data suggest that the PHA swelling response may not be considered as the only consequence of processes of specific and induced immunity –T lymphocytes proliferation- but also of constitutive and nonspecific immunity –heterophiles and monocytes phagocytosis. We propose the extensive use of PHA-skin test as an optimal technique to assess immunocompetence.

Reference levels for corticosterone and immune function in farmed saltwater crocodiles (Crocodylus porosus) hatchlings using current Code of Practice guidelines

“…In contrast to the BKAs, PHA injection may measure both subsets of the immune system. The primary PHA injection mainly measures the pro-inflammatory, phagocytic potential of the innate immune system, whilst the swelling from subsequent injections may provide insight into acquired immunity via immunologic memory (Finger et al, 2013;Martin et al, 2006;Salaberria et al, 2013;Vinkler et al, 2010). Unexpectedly and contrary to our previous findings (Finger et al, 2013), the animals used herein showed no immunologic memory (i.e., subsequent injections did not increase swelling) although there was a significant effect of sampling implying an age and/or seasonal response to antigenic injection.…”

Secondary phytohaemagglutinin (PHA) swelling response is a good indicator of T‐cell‐mediated immunity in free‐living birds

“…Salaberria et al . ). In our study, no differences in proteins between the two different challenges were noticed, but the PHA response was significantly correlated with plasma protein levels, highlighting the innate components of the immune response.…”

Sex-Specific Effects of High Yolk Androgen Levels on Constitutive and Cell-Mediated Immune Responses in Nestlings of an Altricial Passerine

“…These common results in males could be interpreted on the light of common components in the innate and adaptive axes of the immune system (Forsman et al 2010;Vinkler et al 2010). In fact, some studies have shown that the PHA swelling response is an integration of both specific and induced immunity and also of constitutive and nonspecific immunity (Martin et al 2006a;Salaberria et al 2013). However, contrary to lysozyme activity, CMI was also influenced by several variables.…”

“…It is not possible to directly compare those patterns with those reported here because here we have used a measure of the external swelling response, which involves not only proliferation of T-cells but also the secretion of proinflammatory cytokines that recruit and activate effector cells and phagocytes such as basophils, heterophils, and macrophages (Martin et al 2006a;Salaberria et al 2013) and thus involves both innate and adaptive components of the immune system (Stadecker et al 1977;Bílková et al 2015).…”