Role of Immune Factors in Protection of Mammary Gland

Abstract

Humoral and cellular defense mechanisms in the mammary gland play an important role in protection against infection. Opsonization of invading microorganisms is considered the most important function of immunoglobulins in mammary secretions. Bacteria also can be opsonized by complement and antibody or by direct attachment of complement activated through the alternate pathway. Opsonized microorganisms with immunoglobulin G and complement possess a high affinity to phagocyte Fc or complement (C3b) receptors, respectively, receptors promote phagocytosis whereas complement C3b receptors are responsible for attachment of bacteria to phagocytes. Attachment of bacteria to phagocytes initiates phagocytosis and stimulates intracellular microbicidal function. Certain microorganisms can survive within phagocytes despite stimulation of microbicidal function. These microorganisms, however, may be killed by phagocytes activated with lymphokines. Lymphokines, produced by sensitized lymphocytes challenged with specific antigen, induce rapid attraction of leukocytes into lesions. Their immobilization in situ, as well as activation of microbicidal mechanisms of phagocytic cells, results in killing intracellular parasites. Therefore, sensitized lymphocytes in the mammary gland play an essential role in protection against invading pathogens. Milk presents a less than optimum environment that inhibits phagocytic and microbicidal activities of leukocytes in the mammary gland. These problems are discussed with respect to prevention of intramammary infections. © 1983, American Dairy Science Association. All rights reserved.