«MILK: IMMUNE PROTECTION» 21

Abstract

Human milk is a rich source of microbial specific immunoglobulins, immunoregulatory and proinflammatory cytokines, B and T lymphocytes and other effector cells, non-immunoglobulin proteins, carbohydrates, lipids, and a variety of oligosaccharides and enzyme products. Studies carried out to date in a number of laboratories have provided extensive characterization of the temporal kinetics and antibodies specificity of secretory IgA, the principal immunoglobulin found in human milk. Considerable evidence is available to suggest that milk antibodies provide protection against many pathogens. Antibody activity has been demonstrated against bacterial agents such as shigella, salmonella, V. Cholerae, Hemophilus influenzae type B, Helicobacter pylori; viruses such as rubella, respiratory syncytial virus, poliovirus, cytomegalovirus, rotavirus and HIV. Antibodies in the milk also appear to transfer anti-idiotypic immunity in the breast feeding neonates. Non immunoglobulin proteins such as lactoferrin, lysozyme, fibronectin, mucins, and oligosaccharides, lipoproteins and a number of lipids moieties have been detected in milk. These products participate in a variety of defense mechanisms against bacteria, viruses and parasitic agents. The milk T cells display phenotypic markers of activation, including the expression of CD25, CD45RO, and HLA-DR. As a result, these cells in general respond poorly to in vitro stimulation with phytohemagglutinin. However, milk cells are effective producers of interferon γ. The in vivo role of lymphocytes in human milk is uncertain. Mucous membrane sites in the upper alimentary and respiratory tract seem to be potential sites for interaction with human milk cells. It is of interest to note that very small numbers of memory T cells are detected in early infancy. It is possible that maternal memory T cells in milk compensate for the development delay in their production in the infant. There is also evidence from experimental animal studies that milk lymphocytes or their soluble products enter tissues of the neonate. Finally, a number of cytokines have been identified to human milk. These include IL-1β, IL-6, TNF-α, IFN-γ, IL-8 and IL-10. However, their role in mediating regulation of immune function or inflammation in the neonate remains to be determined.