Figure 1.

Spirochetemia with Bt1 and Bt2 in Rag1^−/− and Igh6^−/− mice. Blood was harvested by cardiac puncture from groups of six Igh6^−/− or Rag1^−/− mice each infected throughout 4 weeks. Spirochetes were counted by phase-contrast microscopy and shown as median/μl plasma (linear scale). The spirochetemia was significantly higher with Bt2 (circles) than Bt1 (triangles) in both Igh6^−/− and Rag1^−/− mice and with Bt2 in Rag1^−/− compared with Igh6^−/− mice. **P < 0.01 (Mann-Whitney U-test).