Non-antibody-containing fractions of breast milk inhibit epithelial attachment of Streptococcus pneumoniae and Haemophilus influenzae

Urinary excretion of lactose and oligosaccharides in preterm infants fed human milk or infant formula

At present, not much is known about the absorption and metabolism of human milk (HM) oligosaccharides in term and preterm infants. We investigated the renal excretion of lactose and complex oligosaccharides in preterm infants fed HM (n = 9, mean actual body weight 2290 g) or a cow's milk-based infant formula (n = 9, mean actual body weight 2470 g). We found that the renal excretion of lactose in HM-fed infants was slightly lower than in formula-fed infants (14.0 +/- 7.4 versus 20.4 +/- 8.7 mg kg-1 day-1, mean +/- SD). The excretion of neutral sugars deriving from oligosaccharides was similar in HM-fed and formula-fed infants (3.8 +/- 2.1 versus 2.9 +/- 0.9 mg kg-1 day-1); the difference between means was not statistically significant. The separation and characterization of oligosaccharides by high-pH anion exchange chromatography with pulsed amperometric detection (HPAE-PAD) and subsequent analysis by fast atom bombardment-mass spectrometry (FAB-MS) revealed a more complex pattern in HM-fed infants compared to the formula-fed group. Lactose-derived oligosaccharides characteristic for HM (e.g. lacto-N-tetraose, and lacto-N-fucopentaoses I and II) were excreted in HM-fed but not in formula-fed infants. These results indicate that nutrition has a significant impact on the oligosaccharide composition in urine of preterm infants.

[Structural and functional aspects of oligosaccharides in human milk]

About a century ago, pediatricians observed that in feces of breast-fed infants, compared to those of bottle-fed infants, Bifidobacterium bifidum was the predominant microorganism. It was shown thereafter that aminosugar-containing oligosaccharides are growth factors for a specific strain of Bifidobacterium. Meanwhile, more than 130 lactose-derived oligosaccharides have been identified in human milk. Some of these oligosaccharides like Lacto-N-Tetraose and Lacto-N-Fucopentaose I and II do not occur in minute amounts but in concentrations up to 1-2 g/L. As the total amount of complex oligosaccharides is between 3-6 g/L those components have to be considered as major human milk constituents. There is striking evidence that human milk oligosaccharides are potent inhibitors of bacterial adhesion to epithelial surfaces, an initial stage of infective processes. Therefore, these oligosaccharides are considered to be soluble receptor analogues of epithelial cell surfaces participating in the non-immunological defense system of human milk-fed infants.

Evaluation of sampling sites for detection of upper respiratory tract carriage of Streptococcus pneumoniae and Haemophilus influenzae among healthy Filipino infants

Two sampling techniques, nasal swabbing and oropharyngeal swabbing, for detection of the upper respiratory tract carriage of Streptococcus pneumoniae and Haemophilus influenzae were studied prospectively with 296 healthy Filipino infants at various ages: 6 to 8, 10 to 12, 14 to 17, 18 to 22, 32 to 39, and 46 to 65 weeks. In all age groups S. pneumoniae was isolated significantly more often (P < 0.0001) from the nasal site than from the oropharyngeal site. H. influenzae was found equally often at both sites.

Interaction of pneumolysin-sufficient and -deficient isogenic variants of Streptococcus pneumoniae with human respiratory mucosa

Streptococcus pneumoniae is the most common cause of community-acquired pneumonia, and pneumolysin, a hemolytic toxin, is thought to be an important virulence factor. We have studied the interaction of a pneumolysin-sufficient type II S. pneumoniae strain (PL+) and an otherwise identical pneumolysin-deficient derivative (PL-) with human respiratory mucosa in an organ culture with an air interface for up to 48 h. Ciliary beat frequency (CBF) was measured by a photometric technique, and adherence to and invasion of the epithelium were assessed by scanning and transmission electron microscopy. PL+ and PL- caused a progressive fall in CBF compared with the control which became significant (P < 0.01) at 24 h for PL+ and at 48 h for PL-. At 24 h, there was a significant increase in the percentage of the mucosa of the organ culture that was damaged for PL+ compared with the control (P < 0.01) and PL- (P < 0.02). At 48 h, there was a significant increase in mucosal damage for both PL+ (P < 0.005) and PL- (P < 0.05) compared with the control. At 24 and 48 h, PL+ and PL- adhered predominantly to mucus and damaged cells. PL+ infection alone caused separation of tight junctions between epithelial cells, and at 48 h PL+ cells were adherent to the separated edges of otherwise healthy unciliated cells. PL+ and PL- both caused damage to the epithelial cell ultrastructure. S. pneumoniae infection caused patchy damage to the respiratory mucosa and a lowered CBF. These changes were more severe and occurred earlier with the pneumolysin-sufficient variant.

Anti-inflammatory systems in human milk

Human milk is characterized not only by a complex host defense system that prevents the colonization and proliferation of common microbial pathogens that may pervade the alimentary tract and respiratory tract of the infant but also by a paucity of inflammatory agents and an array of anti-phlogistic factors. Clinical observations support the notion that the protection provided by human milk involves not only antimicrobial factors, but also anti-inflammatory agents. The major anti-inflammatory agents include enzymes that degrade mediators of inflammation, anti-proteases, lysozyme, lactoferrin, secretory IgA and a number of antioxidants including cysteine, ascorbate, alpha-tocopherol, and beta-carotene. It is pertinent that most of these factors are either absent or poorly represented in cow's milk or other artificial feedings that substitute for breast feeding and that the attainment of adult serum levels of some of these antioxidants in early infancy is dependent upon breast feeding. It may be that the provision of these antioxidants may help to protect the recipient's developing immunologic system which is quite susceptible to oxidant damage. The absence of breast feeding will thus deprive the infant of valuable protection against common enteric-respiratory disorders and their inflammatory consequences. It should be pointed out that the protective systems in human milk including the anti-inflammatory components may not be completely delineated, and that little is known of the in vivo fate of the factors and precisely how they protect the recipient. Those questions should form the basis of important research in the next decades.

Mucosal immunity: the immunology of breast milk

The mammary glands represent one part of the mucosal immune system, a definable, subunit of humoral and cellular immune functions in man that appears to have developed particular qualities well suited to guard our interface with the environment. As our understanding of secretory immunoglobulins and lymphocyte migration patterns continues to develop, the immunologic components found in breast milk appear increasingly likely to play a specific immunologic role in the protection of the nursing infant. The biologic basis for the observed protective effect of breast-feeding is reviewed with an emphasis on the mechanisms involved in the development and maintenance of mucosal immunity in general.

Prolonged exclusive breast-feeding results in low serum concentrations of immunoglobulin G, A and M

Serum levels of IgG, IgA and IgM were measured in 198 infants at ages 2, 4, 6, 9 and 12 months. By age 9 months 30 infants were still exclusively breast-fed; their IgG and IgM levels were significantly lower than those of infants weaned early to formula (before age 3.5 months). By 12 months 6 infants were still exclusively breast-fed; their IgA levels were by then also similarly lower. There was no significant difference in the number of infections experienced by these groups of infants. After 2 months on formula feeding, the IgG and IgM levels of the infants who were exclusively breast-fed for 9 months had caught up with the levels of the infants weaned early to formula. Only at 12 months of age prealbumin levels of the exclusively breast-fed infants showed a positive correlation to IgG and IgA levels; no correlation was found between immunoglobulin levels and levels of serum iron and zinc.

Anti-inflammatory properties of human milk

An hypothesis was developed which predicts that human milk protects against infections of the alimentary tract of the breast-fed infant by non-inflammatory mechanisms. Human milk is poor in the initiators and mediators of inflammation and rich in anti-inflammatory agents. Furthermore, many of the anti-inflammatory agents are comparatively resistant to digestive enzymes and therefore might be expected to remain active in the gastrointestinal tract of the recipient. Further studies of these factors in in vivo models will be required to validate the hypothesis.