Development of the IgA System in the Mammary Gland

Abstract

The specificity of the IgA antibodies in milk is puzzling if the secretory immune system is viewed in strictly local terms, i.e., synthesis of antibodies by plasma cells in a secretory site in response to antigen impinging on that site. Milk is known to contain IgA antibodies directed toward antigens which do not directly contact the mammary gland but which do exist in the gastrointestinal tract (1–3). The existence of such antibodies could be explained by transport from the serum, for which evidence is lacking, or by stimulation of immunocytes resident in the mammary gland by antigens absorbed from the intestine and reaching the mammary gland via the blood. Evidence against this latter possibility has been gathered by Montgomery et al. (4) and Goldblum et al. (1), who instead proposed that immunocytes presensitized to antigens of the gastrointestinal tract might migrate to the mammary gland from the gut associated lymphoid tissue (GALT). This could account for the, presence in milk of antibodies to such antigens. The fact that these IgA antibodies are not absorbed to any great extent from the intestinal tract of suckling infants (5–7) and must, therefore, exert their beneficial effects therein would be entirely consistent with this scheme.