Effects of lead shot ingestion on constitutive immune function of red-legged partridges

Abstract

The effects of toxic levels of Pb are diverse and represent several functional systemic alterations. Although the effects of exposure to Pb on the immune system of mammals, and especially in humans, have been extensively studied, little is known about how this heavy metal affects the constitutive immune function in birds. Pb intoxication may be a major problem for birds as they accidentally feed on Pb shots that are confounded with grit particles. We present a preliminary study based on different tests to assess changes in innate immune response of red-legged partridges (Alectoris rufa) subjected to Pb shots. We used four experimental groups (0-9 Pb shots) with six replicates each. A marginally significant lethal effect was detected for the highest Pb treatment (60% mortality; p=0.057). Among survivors, decrease in body mass after Pb exposure affected especially to females. Blood samples were obtained from the survivors 25 days after exposure. We compared blood Pb levels, analyzed by Atomic Absorption Spectrophotometry with graphite furnace, with different parameters indicative of the innate immune response. The ratio between lymphocytes expressing CD4 and CD8 membrane receptors, analyzed by flow cytometry, was affected by the interaction between treatment and sex in a less than significant manner (p=0.060). Haematocrit, serum lysozyme concentrations, bactericidal activity of the whole fresh blood and the ratio heterophils/lymphocytes were unaffected by the exposure to Pb. Our results highlight the necessity to analyze several parameters to asses the immunotoxicity of a substance. Nonetheless, these and other tests should be repeated with a larger sample size to obtain meaningful results. Analyzing constitutive immune function is important in wild populations as it represents the organism's ability to display a quick response against opportunistic pathogens.