CD40LG and infection: Assessing antibody responses generated in IgH-allotype chimeric mice during a T. gondii infection revealed the presence of B-1 derived IgM-a antibodies that had low reactivity to T. gondii at days 14 and 30 post-infection, but the majority of highly reactive parasite-specific IgM-b was derived from the B-2 compartment (Fig 4D).