It has been difficult to perform cytokine studies for many wildlife and nontraditional species because of a lack of immunologic reagents at the protein level. Recently, simple and rapid assays for quantifying mRNA expression by real-time reverse transcription–polymerase chain reaction (RT-PCR) have been used for analysis of cytokine profiles in humans and other mammalian species. This report describes the development and application of real time RT-PCR to measure the expression of several important elk (Cervus elaphus) cytokine mRNAs, including interleukin (IL)-2, IL-4, IL-10, IL-12p40, interferon-gamma, tumor necrosis factor (TNF)- α, and the enzyme-inducible nitric oxide synthase, all of which are involved in immune responses and regulation. For the broadest potential application of the assay, primers and probes were designed using consensus sequences from several species of interest. To obtain standardized quantitative results, external controls consisting of a DNA template for each target gene were used to generate linear standard curves over a 6 to 8 log range with detection of as few as 10 copies of amplicon per reaction. Sample-to-sample variation in the efficiency of the RT, as well as in the quantity and quality of the starting RNA, was compensated for by normalizing the results to the endogenous housekeeping gene β2 microglobulin. The assay was evaluated by monitoring the kinetics of cytokine mRNA synthesis induced by mitogenic and antigenic stimulation of peripheral blood mononuclear cells (PBMCs) from Mycobacterium bovis–infected elk. Concanavalin A–stimulated PBMCs demonstrated a rapid but transient increase in cytokine mRNA expression following in vitro mitogenic activation with optimal mRNA induction observed after 4 to 16 hr. The PBMCs stimulated with the mycobacterial recall antigen, bovine-purified protein derivative (PPD-bovis), demonstrated variable mRNA induction kinetics for each cytokine. Whereas PPD-bovis optimally induced IL-2 mRNA after 8 hr of in vitro stimulation, longer in vitro stimulation times were necessary for the optimal induction of IL-4 and TNF- α mRNA (up to 48 hr). We demonstrate real-time RT-PCR to be a rapid, sensitive, and reproducible technique, which will make it a valuable tool in the study of immunologic responses and cytokine profiles of cervids and other nontraditional livestock and wildlife species.
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Vol. 42 • No. 2