THE POTENTIAL FOR RECRUITING IMMUNE-RESPONSES TOWARD TYPE-1 OR TYPE-2T-CELL HELP

The design of vaccine strategies in general, and those for malaria in particular, need to take into account the balance of T helper subsets (TH) they induce. The TH1 cells, which secrete interferon-gamma and in terleukin-2 (IL-2), are associated with cell-mediated immunity (CMI), rather than humoral responses, and afford protection against intracell ular infections, including those caused by parasites. In contrast, The TH2 cells secrete IL-4, IL-5, and IL-10, elicit high titer antibody r esponses, provide poor CMI, and are often correlated with susceptibili ty to infection. Depending on the type of TH cell bias required, it is possible to manipulate the immune response to a protein/peptide by 1) using different adjuvants, 2) conjugating the protein to various carr iers, 3) immunizing in the presence of cytokines, or 4) using alternat ive routes of administration. To apply these approaches to malarial va ccines, it is necessary to identify which stage(s) of the parasite to target and what type of TH cell bias is protective against that partic ular stage. We favor using carriers such as Brucella abortus, which fo cus the antigen on a specific particle and which can trigger a TH1 cel l response.