Dengue has recently been defined by the World Health Organization as a major international public health concern. Although several vaccine candidates are in various stages of development, there is no licensed vaccine available to assist in controlling the further spread of this mosquito borne disease. The need for a reliable animal model for dengue disease increases the risk to vaccine developers as they move their vaccine candidates into large-scale phase III testing. In this paper we describe the cellular immune responses observed in a human challenge model for dengue infection; a model that has the potential to provide efficacy data for potential vaccine candidates in a controlled setting. Serum levels of sIL-2Rα and sTNF-RII were increased in volunteers who developed illness. Supernatants from in vitro stimulated PBMC were tested for cytokines associated with a T_H1 or T_H2 T-cell response (IL-2, TNF-α, IFN-γ, IL-4, IL-10, IL-5) and only IFN-γ was associated with protection against fever and/or viremia. Interestingly, IFN-γ levels drop to 0 pg/mL for volunteers who develop illness after challenge suggesting that some mechanism of immunosuppression may play a role in dengue illness. The human challenge model provides an opportunity to test potential vaccine candidates for efficacy prior to large-scale phase III testing, and hints at a possible mechanism for immune suppression by dengue.