Figure 8 Cytokines with potential applications as adjuvants in vaccines. Both IL-1 and IFN-γ cause leukocytes to be attracted to and accumulate at a source of antigen, e.g. a vaccine injection site. IL-1 increases the expression of costimulatory molecules on antigen-presenting cells (APCs) and IL-2 receptors (Il-2R) on T cells. IFN-γ increases the expression of MHC molecules and costimulatory molecules on APCs. IL-2 is required for T-cell division, so it enhances cell-mediated immunity.