Role of Immune Factors in Protection of Mammary Gland

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Abstract
Humoral and cellular defense mech- anisms in the mammary gland play an important role in protection against infection. Opsonization of invading mi- croorganisms is considered the most important function of immunoglobulins in mammary secretions. Bacteria also can be opsonized by complement and anti- body or by direct attachment of com- plement activated through the alter- nate 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 respon- sible for attachment of bacteria to phagocytes. Attachment of bacteria to phagocytes initiates phagocytosis and stimulates intracellular microbicidal function. Cer- tain microorganisms can survive within phagocytes despite stimulation of micro- bicidal function. These microorganisms, however, may be killed by phagocytes activated with lymphokines. Lympho- kines, 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 mech- anisms of phagocytic cells, results in killing intracellular parasites. Therefore, sensitized lymphocytes in the mammary gland play an essential role in protection against invading pathogens.