Identification of a cell surface glycoprotein family of olfactory receptor neurons with a monoclonal antibody

Abstract

A monoclonal antibody (Mab) has been developed which recognizes a family of cell surface glycoprotein found in high levels of rat olfactory receptor neurons. This Mab, designated 2B8, was produced by the fusion of X63-Ag8.653 myeloma cells and spleen cells of a mouse immunized with PC12 rat pheochromocytoma cells. Immunofluorescence analyses of cryostat sections of neonatal olfactory epithelium show prominent 2B8 binding to receptor neurons. Within the olfactory bulb only the glomerular and olfactory nerve layers show 2B8 binding. All other neural structures in the main olfactory bulb have background levels of reactivity. Analyses of 2B8 binding to particulate protein preparations from several central and peripheral nervous system components demonstrated highest 2B8 antigen specific activity in olfactory bulb and epithelium and detectable levels in dorsal root ganglia (DRG), whole cerebrum, cerebellum, and brainstem. However, 2B8 antigen could not be detected in non-olfactory structures by immunofluorescence. Some non-neural tissues also had the ability to bind 2B8 Mab in the particulate protein radioimmunoassay. In order to compare the 2B8-reactive molecules found in each tissue, Mab was applied to polyacrylamide gels of unlabeled membrane proteins. A family of molecules with diverse molecular weights was found. Some were unique to individual tissues whereas others were shared among tissues. Olfactory bulb and epithelium had a unique band with M(r) = 215,000 and another band with M(r) = 142,000. The 142,000-dalton band was also found with PC12 cells. PC12 cells also had several bands of lesser molecular weight, including 51,000 and 43,000. Testes membranes had immunoreactive bands only at M(r) = 46,000 and 43,000. Bone marrow, perinatal liver, and DRG each expressed a single 2B8-reactive band with M(r) = ~ 114,000. Salivary gland had four reactive bands, two common to it and only PC12 cells, the 114,000-dalton band which is similar to that found in adult rat bone marrow and DRG, and a unique band at M(r) = 152,000. 2B8 immunoprecipitates of olfactory bulb and epithelium were analyzed for glycosyl groups by lectin reactivity. Wheat germ agglutinin and Ricinus communus agglutinin I bound the 2B8 antigens using two distinct assay methods. This suggests that the 2B8 antigens recognized in the olfactory system are glycoproteins having sialic acid and D-galactosyl components. In summary, the 2B8 Mab recognizes a group of glycoproteins which are the first identified cell surface components of olfactory receptor neurons. 2B8 immunofluorescence reactivity in the nervous system is found only on cells of the olfactory system. Although non-neural tissues have 2B8 immunoreactivity, the molecules recognized differ in apparent molecular weight from those detected in olfactory structures.