Although IgM−/− mice survived a few days longer when re-infected on day 10 with the homologous VSG-expressing AnTat 1.1 parasite, as compared to re-infection using non-homologous VSG-expressing MITat 1.4 parasites (Fig. 4F), this prolonged survival in IgM−/− mice (MS = 12 days) was much less pronounced than the prolonged survival obtained in WT mice, where re-challenge on day 10 did not result in accelerated mortality at all (Fig. 4D). The gene discussed is CD40LG; the disease is infection.