components in human milk to kill microbial pathogens. High concentrations of this protein are found in human milk throughout lactation (Butte et al., 1984b; Goldman et al., 1982, 1983a,b), whereas concentrations in cow's milk are very much lower. Like many other host resistance factors in human milk, lysozyme is relatively resistant to proteolysis and to denaturation resulting from the high acidity within the stomach.
Fibronectin, a protein that enhances phagocytosis, has recently been found in human milk (Friss et al., 1988). Serum levels of this protein are higher in breastfed than in nonbreastfed infants, but that finding cannot be explained solely by the amount of fibronectin in human milk.
Very low levels of the components of the classical and alternative pathways of the complement system have been found in human milk (Ballow et al., 1974; Nakajima et al., 1977). With the exception of the third component of complement (C3), these levels are unlikely to generate inflammation.
Few studies have addressed whether the nutritional status of women affects the immunologic composition of their milk. In a study of the milk from economically privileged and underprivileged women from Guatemala (N = 86) and Ethiopia (N = 12) and privileged women from Sweden (N = 64), Cruz and associates (1982) compared the concentrations and daily output of secretory IgA and secretory IgA antibodies to somatic antigens to serotypes of E. coli. Although it was implied that the underprivileged women were more poorly nourished, indices of nutritional status were not reported. Somewhat similar studies were conducted in India by Reddy et al. (1977) and Reddy and Srikantia (1978). They found no differences in the levels of IgA, IgM, IgG, lactoferrin, or lysozyme in the colostrum from well nourished and poorly nourished women. In that study, poor nutritional status was defined by low body weight and by low weight-to-height ratios. In a study conducted in India, Narula and colleagues (1982) found lower levels of IgG but similar levels of IgA in colostrum from well nourished and poorly nourished women.
A study that more completely defined maternal nutritional status was conducted with 23 Columbian women during the first 2 months of lactation (Miranda et al., 1983). Malnutrition was characterized by lower weight-to-height ratios and by lower creatinine-height indices and serum concentrations of total proteins, albumin, IgG, and IgA. The levels of albumin and IgG in the milk were much lower in malnourished women than in well nourished women. There were also significant but less striking decreases in IgA and C4 levels in milk from malnourished women, whereas no differences were found in C3 and lysozyme levels or in specific antibodies to respiratory syncytial virus.
More recently, Robertson and coworkers (1988) investigated the effects of maternal nutrition upon the avidity of secretory IgA antibodies to E. coli polysaccharides and diphtheria toxin in human milk. Decreased avidity was found in antibodies from the malnourished group.
In summary, the effects of maternal nutritional status upon the immunologic