Influence of Early Weaning and Dietary Fat on Immune Responses in Adult Rats

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Abstract
Equal numbers of female rats, either prematurely weaned at 14 days of age or allowed to nurse for 21 days, were pair-fed a diet containing either vegetable oil or cholesterol-enriched animal fat for 95 days. Thereafter all animals received the animal fat diet until 11 months of age. Rats were then immunized with sheep erythrocytes and the antibody response quantified. There was no significant effect of early weaning or diet on the number of plaque-forming splenocytes or on serum hemolysins. A significant positive correlation between HDL cholesterol and both plaque-forming cells and hemolysin titres was detected in the groups fed animal fat. Significant impairment in splenocyte blastogenic response to phytohemagglutinin was observed in rats receiving animal fat prior to 95 days. Separate groups of rats were infected 5 days before death with Listeria monocytogenes. Splenocyte blastogenesis was impaired in the group fed animal fat to a degree similar to that observed in uninfected rats fed the same diet, and there were increased numbers of bacteria recovered from the spleen and kidney of animals whose early diet contained animal fat. We conclude that the fat content of the early postweaning diet has an impact on immune responses which persists into adulthood.