Cytokine gene expression after in vivo primary immunization with goat antibody to mouse IgD antibody

Cytokines are important mediators of effector lymphoid cell function during an immune response, but their expression during an in vivo immune response has not been well documented. We analyzed the kinetics of cytokine gene expression during the course of an in vivo primary immune response to goat antibody to mouse IgD antibody. Total RNA was purified from spleens taken from freshly killed BALB/c mice 1 to 7 days after immunization. The reverse transcriptase polymerase chain reaction was used to evaluate the expression of seven cytokine genes, all of which encode cytokines that are secreted by T cells and are important in T and/or B cell activation and differentiation. These were IFN-gamma, IL-2, IL-4, IL-5, IL-6, IL-9, and IL-10. IL-2 and IL-9 exhibited an early elevated expression at days 2 to 3, and declined as the expression of IL-4, IL-6, IL-10, and IFN-gamma increased. In contrast, IL-5 gene expression showed little change, exhibiting a similar pattern to the housekeeping gene, hypoxanthine-guanine phosphoribosyl transferase. Cell sorting of CD4+ and CD4- cells at day 3 and day 5 after immunization revealed that CD4+ cells were the predominant source of the elevated cytokines (with the exception of IL-6). Our results demonstrate a specific and highly reproducible cytokine gene expression pattern during the course of a primary in vivo immune response that is marked by an absence of a clear-cut Th1/Th2 dichotomy.