Avian Immunotoxicology

Abstract

Methods for studying the avian immune system have matured during the past two decades, with laboratory studies predominating in earlier years and field studies being conducted only in the past decade. One application has been to determine the potential for environmental contaminants to produce immune suppression, while another research direction is looking at the evolutionary significance of a robust immune system, and the relationship between immune competence and fitness parameters. Laboratory studies of immunosuppression following exposure of birds to environmental contaminants have adapted conventional mammalian methods to the avian immune system, and both lines of research have developed field-deployable measures of immune function. This review describes the avian immune system with emphasis on how it differs from the better known mammalian system, reviews the literature on contaminant-induced immunosuppression, and discusses the work on evolutionary biology of avian immunocompetence. Evidence indicates that the field of avian immunology is technically robust, even for nontraditional species such as passerines, seabirds, raptors, and other free-ranging species. It is now possible to screen chemicals for immunotoxicological properties following the same tiered approach that has been established for mammals. Despite the increased capacity and interest in avian field studies, there has not yet been a reported study of measured immune suppression associated with an avian epizootic. It is more likely that the immune suppression in adult birds resulting from low-level chronic stress (e.g., crowding onto poor quality habitat, food reductions, or climate stress) and (or) environmental contaminants causes slow but consistent morbidity and mortality associated with multiple pathogens, rather than an acute epizootic with a single pathogen. Increased fitness costs associated with such stress may significantly alter genetic diversity and species survival over time.

Complex Interplay of Body Condition, Life History, and Prevailing Environment Shapes Immune Defenses of Garter Snakes in the Wild

“…In this respect, the in vitro lymphocyte proliferation assay used here is a good option for assessment of adaptive immunity because it can be performed with a single small blood sample collected in the field and measures important aspects of acquired immune responses, that is, the ability of lymphocytes to become activated and proliferate upon challenge. Using different mitogens (e.g., PHA, ConA, LPS), different lymphocyte subsets are targeted, providing information on more than one cell type (Fairbrother et al 2004). Although performance of this assay requires a specialized laboratory setting, it can be accomplished through fruitful collaborations among ecoimmunologists and more traditional immunologists, as is generally the case for other measures of immune function (e.g., Matson et al 2005Matson et al , 2006Millet et al 2007).…”

“…Although performance of this assay requires a specialized laboratory setting, it can be accomplished through fruitful collaborations among ecoimmunologists and more traditional immunologists, as is generally the case for other measures of immune function (e.g., Matson et al 2005Matson et al , 2006Millet et al 2007). The lymphocyte proliferation assayas do most assays of immune function-has some limitations in addition to its strengths (Fairbrother et al 2004;Demas et al 2011). In particular, this assay assesses only early steps of acquired immune responses; thus, for a more complete assessment of acquired immunity of animals that cannot be easily recaptured in the wild, additional in vitro assays that measure effector functions such as B-cell antibody production or T-cell cytotoxicity and that also involve a single blood sample could be performed (Fairbrother et al 2004).…”

“…Activation and proliferation of lymphocytes are critical initial steps of acquired immune responses-both cellular, mediated by cytotoxic T-lymphocytes, and humoral, mediated by B-lymphocytes and helper T-lymphocytes-leading to the formation of clones of cells that can more effectively fight the invader (Roitt et al 1998). In vitro lymphocyte proliferation assays are widely employed by immunologists and immunotoxicologists (Froebel et al 1999;Grasman 2002;Fairbrother et al 2004) and can provide val-Immune Defense Strategies of Garter Snakes in the Wild 549 uable insights into the immune function of free-living animals (Palacios et al 2007.…”

Tree Swallows (Tachycineta Bicolor) Nesting on Wetlands Impacted by Oil Sands Mining Are Highly Parasitized by the Bird Blow Fly Protocalliphora Spp.

“…Interestingly, Simon et al (2003) recently showed that Protocalliphora larvae aggregate on the smallest chicks of a brood, which tend to be less immunocompetent than their siblings (Christe et al, 1998). Several environmen-tal contaminants are known to affect the immune system of wildlife (reviewed by Fairbrother et al, 2004). If chemicals present in OPSM were affecting the immune function of nestlings, perhaps parasitic larvae feeding on those nestlings would have greater survival rates than those developing on chicks with normal immune defenses, partly explaining the larger parasitic loads on reclaimed sites.…”

Avian immunosenescence

“…IgM, IgG, IgA and IgY antibodies have been described in birds, but identical roles to mammalian forms have not been confirmed. In avian studies, common measures of in vivo immune function are the phytohemagglutinin (PHA) skin test response and antibody response to foreign red blood cells (Fairbrother et al 2004). The PHA skin test is a T-cell-dependent inflammatory response.…”