CELL-MEDIATED AND HUMORAL IMMUNE-RESPONSES AFTER VACCINATION OF HUMANVOLUNTEERS WITH THE LIVE VACCINE STRAIN OF FRANCISELLA-TULARENSIS

The specific humoral and cell-mediated immune responses of human volun teers vaccinated with the Francisella tularensis live vaccine strain ( LVS) were evaluated. In the search for an optimal antigen to measure t he immunogenicity of the vaccine in an enzyme-linked immunosorbent ass ay, we tested irradiation-killed LVS, an aqueous ether extract of the LVS (EEx), lipopolysaccharide (LPS) from LVS, and a virulent strain (S CHU4). Volunteers were immunized with LVS by scarification. Immunoglob ulin G (IgG) responses to LVS and LPS gave the highest background tite rs when tested with sera from unimmunized volunteers, whereas IgA, IgG , and IgM background titers to EEx and SCHU4 were low. Vaccination cau sed a significant rise (P < 0.01) in IgA, IgG, and IgM titers to all a ntigens tested, except for the IgG response to LPS. Eighty percent of vaccinated volunteers developed a positive IgG response to EEx 14 days postvaccination, while 50% were positive to LVS. By day 14 after vacc ination, 70% of immunized volunteers exhibited a positive response to EEx in an in vitro peripheral blood lymphocyte proliferation assay. EE x, a specific and sensitive antigen for evaluating immune responses of vaccinated volunteers, may be a superior antigen for the diagnosis of tularemia.