Here we show that although immunization with whole saliva induces a humoral response, this immune response is unable to protect mice against infection; in contrast, immunization with a plasmid coding for Ph. sergenti PsSP9 salivary protein induces a Th1 immune response characterized by a strong DTH response, no detectable antibody response, and a high expression ratio of IFN-γ to IL-5 in lymph nodes. The gene discussed is IL5; the disease is infection.