IMMUNOLOGICAL UNRESPONSIVENESS TO HELMINTH PARASITES .2. ANTIBODY RESPONSE AND HYPERSENSITIVITY REACTION ASSOCIATED WITH NIPPOSTRONGYLUS BRASILIENSIS INFECTION IN YOUNG RATS

We have previously shown that in rats infected when under 6 weeks of age with N. brasiliensis worm expulsion occurs only if more than 200 worms are established in the intestine. In such cases, worm expulsion starts later and proceeds at a slower rate than in comparatively infected adult rats stopping when a worm burden of 200 is reached. This relatively large residual infection persists into adult life. In the present paper the antibody status of rats infected when young was examined. Passive protection tests using the serum from such rats showed that protective antibody was produced by rats infected with more than 800 larvae, despite the fact that in these rats worm expulsion did not proceed to completion. It was also found that young rats produced reaginic antibody comparable in time of appearance and titer with similarly infected adults. Allergen production by the worms of the persistent infection was titrated and found to be produced in unreduced amount for at least 40 days after infection. Intestinal mast cell counts of the unresponsive rats were similar to those of infected adult rats. It was concluded that the incomplete expulsive reaction of rats infected when young cannot at present be explained by the absence of protective or reaginic antibodies or by a deficiency in the number of intestinal mast cells. © 1969.