Patterns of Expression of Class I Antigens in the Tissues of Congenic Strains of Rat

A comparative study of expression of class I major histocompatibility (MHC) antigens among lung, spleen, kidney, heart, liver, and brain tissues of the rat was performed. Monoclonal antibodies (MAbs) against RT1A^a determinants were conjugated to ¹²⁵I and applied to frozen sections. Resulting autoradiograms showed antigen reactivity in lymphoid tissue, bronchial and alveolar epithelium, and endothelium of the lung. The Iymphoid tissue of the lung and spleen demonstrated the antigen after shorter autoradiographic exposures than was required for the epithelial components of these organs. The kidneys were heavily labeled over the glomeruli, but less intensely over the tubular epithelium. RT1A antigen content of capillary endothelium of the heart was demonstrable before that of the muscle bundles. In the liver, autoradiographic sections revealed high determinant density in sinusoidal regions. Brain sections show reproducibly low levels of labeling, with the exception of vascular structures. All of these tissues from PVG-RT1^c and PVG-RT1^u animals show only background labeling.