Quantifying phagocytic lymphocytes in ectothermic vertebrates: A simplified technique for assessing immune function

Abstract

Many measures of immune function used in ecoimmunological studies were optimized for endotherms and may not adequately characterize immunocompetence in ectothermic species. Lymphocytes are interpreted as functioning in adaptive immunity despite evidence that large proportions of these cells have innate immune functions, including phagocytosis, in ectotherms. We modified previously published protocols to remove many barriers that inhibited the wide application of assays to quantify phagocytic activity in lymphocytes. These barriers included the use of species-specific reagents, high cost and incompatibility with field work. We statistically compared published methods to our simplified technique using blood samples collected from tortoises. We show the efficacy of the new technique and offer an outline for optimizing these methods for different species and to address a wide variety of ecoimmunological questions. A full understanding of immune function in ectothermic vertebrates is needed to comprehend complex epidemiological patterns. As our assay disentangles the relationship between effector cells (lymphocytes) and their function (phagocytosis), these methods provide a foundation for more thorough analyses of ecoimmunological patterns.