DIETARY-PROTEIN AND ZINC RESTRICTIONS INDEPENDENTLY MODIFY A HELIGMOSOMOIDES-POLYGYRUS (NEMATODA) INFECTION IN MICE

The effects of dietary protein and zinc restrictions on Heligmosomoide s polygyrus were compared following primary and challenge infection in female BALB/c mice fed either control (24%), marginal (7%) or low (3% ) protein combined with either high or low zinc (60 or 3 mg Zn/kg diet ). Dietary protein restriction (3%) resulted in significantly lower bo dy weight gain. As well, blood urea nitrogen (BUN) significantly decre ased with decreasing dietary protein level. However, neither plasma al bumin concentration nor relative thymus or spleen weights were reduced . Marginal zinc deficiency was confirmed by significantly lower tibia and liver zinc concentration, but food intake, body weight gain, relat ive thymus and spleen weights, and alkaline phosphatase activity were not altered. On day 29 post-primary infection, worm burdens were signi ficantly higher in mice fed either marginal or low protein and in mice fed a low zinc diet, while parasite egg output was significantly high er in mice fed both low protein and low zinc diets. Immune status was compromised in mice fed low protein (significantly lower serum IgG1 an d lower eosinophilia), and in mice fed low zinc diet (significantly lo wer eosinophilia). Early in the infection, IgE titres were elevated in mice fed low protein or low zinc, but IgE titres declined to levels l ower than the control diet groups after 14-21 days. On day 29 post-cha llenge infection, worm burdens and parasite egg output were significan tly higher in mice fed low protein, whereas the other groups had expel led almost all parasites. Dietary restriction had no effect on serum I gE. Significantly reduced. serum IgG1 titres and eosinophilia in mice fed 3% protein supported the view that low dietary protein but not low zinc increased host susceptibility to H. polygyrus by compromising ho st immune function following reinfection in immunized mice.