Expansion of blood leukocytes in infected IFN-γ −/− mice. Leukocyte counts (in cells per μL) were measured at different times after infection (abcissa). Closed symbols are IFN-γ +/+ mice, open diamonds are IFN-γ −/− mice. Results are typical of numerous experiments and are further documented in Tables 1 and 2 and Fig 4.