Production of monoclonal antibodies against a novel glycoprotein synthesized and secreted by dog thyroid C-cells.

A monoclonal antibody (MAb) that reacted only with thyroid C-cells was raised against cell suspensions from dog thyroid glands, to examine a glycoprotein secreted by C-cells. After chronically-induced hypercalcemia and administration of an anti-thyroid drug, reaction products for the antibody markedly decreased in C-cells, coinciding with alterations in calcitonin immunoreactivity. The antigen recognized by the MAb appears to be a secretory protein. The MAb reacted with C-cells from a wide variety of mammalian species, including rats, mice, hamsters, cattle, cats, rabbits, and monkeys. Furthermore, tumor cells of human medullary thyroid carcinoma, which is derived from C-cells, were immunoreactive to the MAb. Exceptionally, C-cells from guinea pigs and pigs were not stained with the MAb. No crossreactivity was observed in any of the dog tissues examined. Immunoblot analysis demonstrated that the MAb recognized a single prominent band at a molecular weight of approximately 79,000. The 79 KD band reacted with various digoxigenin-labeled lectins, including GNA, DSA, SNA, and MAA; it is a glycoprotein containing mannose, N-acetylglucosamine, and sialic acid. Dog thyroid C-cells were also densely stained with these lectins. The results indicate that thyroid C-cells synthesize and secrete a specific glycoprotein in addition to peptide hormones.