Mice immunized with VSV vaccine vectors produce IL-1b systemically and at the injection site Both IL-1a and IL-1b are regarded as pro-inflammatory cytokines, but IL-1b rather than IL-1a has been more commonly associated with symptoms such as weight loss and fever that are induced by infection with a live virus or other immune stimulus [16, 17] . To determine whether intramuscular immunization with VSV vaccine vectors induced production of IL-1b in vivo we challenged wild type C57BL/6 mice with rVSV and used an ELISA to quantitate the amount of IL-1b produced locally (at the injection site and in the draining lymph node) and systemically (in the blood). As shown in Figure 2A -C, mice immunized intramuscularly with rVSV had accumulations of IL-1b in the blood, in the quadriceps muscle, and in the popliteal lymph node that drains the quadriceps at 12 and 24 hours after immunization with VSV rwt. These results confirmed that IL-1b was produced in vivo both locally and systemically after intramuscular rVSV challenge, and was consistent with the results of Poeck et al. who found that wild-type mice injected intravenously with rVSV had detectable levels of IL-1b in the serum at six hours after challenge [22] . Our results were also consistent with the hypothesis that IL-1b caused the acute pathology that occurs after immunization with rVSV vaccine vectors, and suggested that reducing the production of IL-1b after rVSV immunization might correspondingly reduce reactogenicity and other undesirable side effects of vaccination.