In vitro studies on the selective binding of IgG from different species to tissue sections of the bovine mammary gland

Abstract

Tissue sections of the mammary gland of cattle provide a sensitive and reproducible model for studying the initial events of the selective transport of bovine IgGs by the acinar epithelium (AE). Mammary tissue was reacted with purified antibody to horseradish peroxidase (HRP) and exposed to HRP. The sites of peroxidase activity were revealed cytochemically. The highly selective binding of IgGs by AE of the colostrum-forming gland but never of the lactating gland was most notable, whereas IgG1 and IgG2 subclasses and IgM and IgA lacked any binding capacity. An inhibition assay showed that the inhibitory capacity of IgGs was abolished by either alanylation or acetylation, whereas binding of IgGs was blocked by both Fab/c and isolated H-chains, but not by F(ab')2, Fab and Fc. The inhibitory pattern suggests that the region on the IgGs molecule involved in binding to the AE receptor may be located within the CH2 domain. In addition, IgG preparations of human, sheep and rabbit origin were found to be equally efficient in inhibiting the binding of IgGs to AE, whereas no inhibition was obtained with nonmammalian (turtle and chicken) IgG. Similarly, human myeloma proteins of the subclasses IgG1 and IgG3 caused complete inhibition, while IgG2 and IgG4 were inefficient. It is suggested that molecular evolution of IgG within mammalian species is accompanied by the conservation of structures fitting to receptors on the cell surface of different species.

The Mammary Gland in Mucosal and Regional Immunity

“…The serum to milk transport of IgG1 appears to be mediated by Fc receptors on alveolar epithelial cells (Kemler et al, 1975;Leary et al, 1982) that could be induced by the administration of estrogens and progesterone to nonpregnant heifers (Smith, 1971). However, such a receptor must also be present in the capillary endothelium.…”

Identification and function of neonatal Fc receptor in mammary gland of lactating mice

“…The mammary gland of cows transmits the IgG1 subclass better than IgG2, with an IgG1/ IgG2 ratio of greater than 10/1 in colostrum [24]. Although little is known about the existence of a bovine ortholog of FcRn [27], this suggests that similar mechanisms for IgG transfer into milk may occur in both mice and cows. Although little is known about the existence of a bovine ortholog of FcRn [27], this suggests that similar mechanisms for IgG transfer into milk may occur in both mice and cows.…”

Structural Evidence for a New IgG1 Antibody Sequence Allele of Cattle

“…Bovine IgG1 has several unique characteristics as this subclass: (1) constitutes 90% of colostral immunoglobulin [10–12] that provides protection to the neonate; (2) is involved in selective transfer [13–15] via FcRn‐like receptor on alveolar epithelial cells of mammary glands [16]; (3) binds to neutrophils similar to IgG2 [17, 18]; and (4) is synthesized locally and released as secretory immunoglobulin on mucosal surfaces [14, 18]. Such properties of cattle IgG1, known for thymus‐dependent immune responses across species, necessitate additional structural analysis as the sequence differences could be of functional consequence, similar to IgG2, in the context of resistance to infections.…”

“…Bovine IgG1 has several unique characteristics as this subclass: (1) constitutes 90% of colostral immunoglobulin [10][11][12] that provides protection to the neonate; (2) is involved in selective transfer [13][14][15] via FcRn-like receptor on alveolar epithelial cells of mammary glands [16];…”