Analysis of the Kinetics and Regulation of Cytokine Gene Expression During the Primary In Vivo Immune Response to Killed Brucella Abortus
Uniformed Services University Of The Health Sciences Bethesda United States
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Cytokines are thought to be important mediators of effector lymphoid cell function, but their expression during an in vivo immune response has not been welldocumented. Based on in vitro studies, immunization of mice with Brucella abortus BA has previously been characterized as a Th1 response, associated with elevated IL-2 and IFN-gamma Th1 cytokines and depressed IL-4 and IL-5 Th2 cytokines. In this study we attempted to determine 1 the Th1 Th2 cytokine gene expression pattern following primary immunization of mice with BA 2 whether cytokines elevated early in the response influence the later cytokine gene expression pattern and 3 whether CD4 T cells or other cell types might contribute to the expected elevation in Th1 cytokines. Total RNA was purified from the spleens of mice 1 hour and 1 to 7 days after BA immunization. A quantitative reverse transcriptase-polymerase chain reaction RT-PCR was used to evaluate the expression of seven cytokine genes, all of which encode cytokines that are secreted by T cells and have been found to be specifically associated with the Th1 or the Th2 response. These were IFN-y, IL-2, IL-4, IL-5, IL-6, IL-9, and IL-10. IL-6 and IL-10 were elevated by 1 hour and IFN-y was elevated by 1 day after BA immunization. Although IL-6 was reduced to baseline levels by 1-2 days, IFN-y and IL-10 remained elevated throughout the time period examined. Similar results were obtained following BA administration in the footpads of mice and analysis of cytokine gene expression in the draining popliteal lymph node, except that the elevation of IL-6 was more prolonged. Cell sorting analysis of spleen cells from BA-immunized mice revealed that although at 1 hour non-T cells were responsible for the increased cytokine expression, by 1 day, Thy-1 cells were the primary source of elevated IL-10 and IFN-y and that CD4 cells expressed elevated IL-10, but not IFN-y.