Transplacental transfer of rodent microfilariae induces antigen-specific tolerance in rats.

Microfilariae are the smallest form in the life-cycle of filarial nematode parasites. They are released by the adult female worms and migrate through the blood and extracellular fluids where they can be transmitted by vectors. A few reports have indicated the possibility of the transmission of microfilarial infection from mother to offspring. We have infected rats with adult females of the rodent filaria, Dipetalonema viteae, and report here that the transfer to D. viteae microfilaria does indeed occur through the placenta. Exposure to specific antigens early in development can readily induce immune tolerance. We observed that a state of reversible immune unresponsiveness occurred in rats as a result of pre- and post-natal exposure to microfilariae and this was associated with impairment of T-cell responses. The induction of tolerance allowed D. viteae infective larvae to reach maturity in the Fischer rat which is otherwise innately resistant to this practice.