Nematospiroides dubius: the course of primary, secondary and tertiary infections in high and low responder Biozzi mice.

Biozzi mice of Selections 1 and 3, each exhibiting either high- or low-antibody responses to a wide range of antigens, were exposed to primary, secondary and tertiary infections of the nematode, Nematospiroides dubius. The course of these infections was followed by monitoring egg output and by examination of the worm burdens on the 14th day after each exposure to the parasite. When exposed to a primary infection, high and low responders were equally susceptible to the parasite, and the egg production of the infections was similar in all groups. However, when the mice were exposed to a 2nd infection of N. dubius, marked differences in the susceptibility of the hosts were seen. The high-responder mice of both Selections 1 and 3 were significantly more resistant to infection, far less adult worms being found in these. Resistance to a 3rd and final infection of the parasite was amplified appreciably in all groups but, again, the high-responder mice were significantly more resistant than the low responders. These results imply that host antibodies play an essential role in immunity to this parasite and that resistance cannot be attributed solely to non-specific macrophage activity or cell-mediated immune reactions, since the latter are equivalent in high and low lines and the macrophages of the Ab/L line of Selection 1 are hyperactive.