11-16 inhibits IL-5 production by antigen-stimulated T cells in atopic subjects

Background: We have previously shown increased expression of the CD4(+) cel l chemoattractant IL-16 at sites of airway allergic inflammation. Little is known about the significance of IL-16 in allergic inflammation and its rol e in allergen-driven T-cell cytokine responses. Because IL-16 interacts spe cifically with CD4(+) T cells, we hypothesized that IL-16 released at sites of inflammation may modulate the pattern of cytokines produced by CD4(+) T cells. Objective: We investigated the effects of exogenous rhIL-16 on cytokine pro duction of PBMCs from atopic and nonatopic subjects in response to antigen and PHA. Methods: Primary cultures of freshly isolated PBMCs from ragweed-sensitive atopic subjects and nonatopic subjects were stimulated with ragweed or PHA in the presence or absence of rhIL-16, Supernatant levels of IL-4, IL-5, an d IFN-gamma were determined by means of ELISA at different time points betw een 2 and 6 days. Effects of IL-16 on antigen-induced cellular proliferativ e responses were determined. Results: No IL-4 protein was detected after antigen stimulation of PBMCs fr om atopic subjects, whereas significant levels of IL-5 were measured on day 6 (median, 534.9 pg/mL). IL-5 secretion was abolished in PBMC cultures dep leted of CD4(+) cells. The addition of rhIL-16 in antigen-stimulated PBMC c ultures significantly reduced the amount of IL-5 released (median, 99.8 pg/ mL; P < .001). Detectable levels of IFN-<gamma> (median, 53.3 pg/mL) were i dentified after antigen stimulation. The addition of rhIL-16 in antigen-sti mulated PBMC cultures significantly increased IFN-gamma levels (median, 255 .6 pg/mL; P < .05). Effects of rhIL-16 appear to be specific for antigen-st imulated PBMCs in atopic subjects because rhIL-16 did not alter IL-5 or IFN -<gamma> production in response to PHA nor did rhIL-16 alter cytokine produ ction in nonatopic normal subjects. Conclusion: These studies suggest that IL-16 can play a role in regulating the production of cytokines seen in allergic states in response to antigen.