IL1B and Splenomegaly: Neutralization of IL-1α, and to a much lesser extent IL-1β, was associated with a significant increase in the mortality of R. typhi-, R. rickettsii-, and R. montanensis-infected mice (Fig. 2A to C) and resulted in the development of splenomegaly (see Fig. S2 in the supplemental material), which correlated with an increase in bacterial loads in the spleen (Fig. 2D).