Immunoglobulins A and G2a in milks of protein- and calorie-restricted dams.

It is well accepted that breast-feeding enhances the ability of newborns and infants to be protected against infection. Maternal nutritional status may affect this passive immunological defense mechanism because of either the change in the volume of milk or the alteration of the immunological components secreted in the milk. Diet restriction in lactating dams has been shown to influence the secretion of immunoglobulin in their milk. We investigated the specific role of caloric or protein restriction on immunoglobulin A (IgA) and IgG2a secretion in the milk of lactating rats. Both calorie- and protein-restricted dams had lower protein levels (milligrams per milliliter) than did the controls during the initial days of lactation (P less than 0.05). The levels (milligrams per milligram of protein) of IgA and IgG were higher in the milk obtained from calorie-restricted dams during the whole lactation period. The amount of IgA in the milk of protein-restricted rats was higher during 21 days of lactation, while the amount of IgG2a was higher only during the first 2 weeks of the lactation period compared with the respective values for the milk from control dams (P less than 0.05). Rats on a protein-restricted diet had lower IgA and IgG2a levels in their milk than those on a calorie-restricted diet at the second half of the lactation period (P less than 0.05). Our data suggest that the diet-restricted dams had a compensatory mechanism to ensure passive immunological protection for their pups during lactation. The compensation was diminished with a protein-restricted diet compared with a calorie-restricted diet.