Since mice infected with KN99α did not survive beyond 19 days, they were not available for leukocyte analysis on day 21 p.i. The total number of leukocytes (i.e., CD45+) in the lungs was significantly higher for mice infected with the cda1Δ2Δ3Δ mutant than for either KN99α-infected or PBS control mice on day 3 p.i. (P < 0.05), which reached similar levels at the later stages of infection (Fig. 3A). This evidence concerns the gene PTPRC and infection.