Breakdown of immunity to Nippostrongylus brasiliensis in lactating rats

The nutritional basis of breakdown of immunity to parasites may be addressed in a rodent model. We hypothesized that lactating rats would show a breakdown of immunity to Nippostrongylus brasiliensis, and that this breakdown of immunity would be sensitive to protein supply. Rats were immunized with 1600 infective N. brasiliensis larvae and subsequently mated. During lactation, these rats were offered foods with 90 (low protein; LP) or 210 (high protein, HP) g crude protein (N×6·25)/kg and re-infected with 400, 800 or 1600 larvae on day 2 post-parturition. Immunized non-reproducing rats were offered a food containing 60 g crude protein/kg and re-infected with 1600 larvae. Seven days after secondary infection, lactating rats had more adult nematodes in their small intestine and nematode eggs in their colon contents than the nonreproducing rats. Protein supply did not affect worm or egg counts, although LP rats carried relatively more female nematodes than the HP rats. All lactating rats had lower intakes than expected from previous studies using similar nutritional protocols. This may have resulted in insufficient protein supply, even for the HP rats, and this could explain the absence of effects of protein supply on egg and worm counts. We conclude that a breakdown of immunity to N. brasiliensis can occur in lactating rats; this strongly suggests that the lactating rat is a suitable model for elucidating a possible nutritional basis of breakdown of immunity to parasites. However, sufficient protein intake must be achieved to address the hypothesis that breakdown of immunity to N. brasiliensis is sensitive to protein supply.