Considering (i) the limited knowledge of the role of individual antibody isotypes in trypanosomiasis control, and (ii) the unclear role of B-cells in the in vivo induction of trypanosomiasis-associated anemia, we used B-cell (μMT) and IgM-deficient (IgM−/−) mice to address these points. The gene discussed is CD40LG; the disease is anemia (phenotype).