Application of the immunogold-silver staining method to localize a mammary-derived growth inhibitor

Suitability of different protein A-gold markers for immunogold-silver staining in paraffin sections

An incubation protocol to immunolabel Lowicryl semithin sections was applied to paraffin probes. To improve the labeling density, colloidal gold complexes of different preparations and sizes were compared. The type of colloidal gold preparation used was found to affect the specificity of the immunostaining. Gold colloid of 5 nm diameter particle size prepared with white phosphorus minimized nonspecific background labeling of beta-casein in paraffin embedded sections of the mammary epithelium of pregnant mice. Gold colloids of 5 nm and 9 nm diameter particle size prepared in varying concentrations of tannic acid generated significant nonspecific staining in similar tissue preparations.

Irregular distribution of mammary-derived growth inhibitor in the bovine mammary epithelium

Localization of a mammary-derived growth inhibitor (MDGI) in the bovine mammary gland was verified by light- and electron-microscopic methods. Expression of MDGI, which is known to inhibit the growth of mammary epithelial cell lines in vitro, was found to be highest in the late pregnant and in the lactating state. A combination of immunohistochemical and immunocytochemical methods with semi- and ultrathin resin sections revealed marked variations in MDGI staining. High MDGI levels were predominantly detectable in epithelial cells with large milk fat droplets. Distinct cell types that were almost free of label could be identified among bovine mammary epithelial cells that always exhibited high MDGI levels. Similar results were obtained when using a serum-free organ culture system in which MDGI was hormonally induced in cell types of comparable differentiation state. The specific occurrence of the growth inhibitor in developing alveoli and certain cell types points to the association between MDGI expression and functional differentiation in the normal mammary gland.