The suppression of rejection of Nippostrongylus brasiliensis in lactating rats: the nature of the immunological defect.

Lactating female rats infected with 3000 third-stage larvae of Nippostrongylus brasiliensis showed significant increases in worm fecundity and total worm burdens when compared with infected nulliparous controls. Statistically significant differences were recorded for each of the three periods of infection, although these differences were of greatest magnitude during Period 3 (16–30 days of infection). Immune mesenteric lymph node cells (100 × 106), obtained from nulliparous female donors on Day 15 of a primary infection, were transferred syngeneically to lactating female recipients. The transferred cells invariably caused suppression of worm fecundity, reduction in the number of eggs per uterus in gravid female worms and rejection of a substantial proportion of worms by Day 10 of a challenge infection in the lactating recipients. The results of this study showed that immune cells were functional in lactating female recipients and that transfer of immune cells repaired the deficit in the rejection mechanism. Mesenteric lymph node cells (100 × 106), obtained from lactating female donors on Day 15 of a primary infection, were transferred syngeneically to nulliparous female recipients. The transferred cells caused suppression of worm fecundity, reduction in the number of eggs per uterus in gravid female worms and rejection of the majority of parasites by Day 10 of a challenge infection in the nulliparous recipients. Clearly, potentially immune lymphoid cells were present in the mesenteric nodes of lactating females at the time that the rejection mechanism was severely impaired. Mesenteric lymph node cells obtained from infected lactating donors were substantially less effective in lactating recipients than in nulliparous recipients. These cells caused the expulsion of 51 per cent of worms by Day 10 in lactating recipients, whereas they caused expulsion of 99 per cent of worms in nulliparous recipients. These observations suggest that the inductive processes of the immune response occur normally, but that differentiation of induced cells to effector cells is impaired in lactating animals.