IL1B and Rickettsiosis: In contrast, transfer of Il-1β−/− BMDMs had an overall lesser effect on the severity of rickettsiosis, as evidenced by a lower mortality rate, smaller spleen size, and lower bacterial burden in Cl2MBP-treated WT mice (Fig. 6A to E; see Fig. S7 in the supplemental material), which is in agreement with our IL-1β Ab neutralization data (Fig. 2).