GENERATION AND CHARACTERIZATION OF MONOCLONAL-ANTIBODIES TO ALVEOLAR TYPE-II CELL LAMELLAR BODY MEMBRANE

Monoclonal antibodies against the limiting membrane of alveolar type I I cell lamellar bodies were obtained after immunization of mice with a membrane fraction prepared from lamellar bodies isolated from rat lun gs. The specificity of the antibodies was investigated with Western bl ot analysis, indirect immunofluorescence, and electron-microscopic imm unogold studies of freshly isolated or cultured alveolar type II cells , alveolar macrophages, and rat lung tissue. One of the monoclonal ant ibodies identified, MAb 3C9, recognized a 180-kDa lamellar body membra ne (lbm180) protein. Immunogold labeling of rat lung tissue with MAb 3 C9 demonstrated that lbm180 protein is primarily localized at the lame llar body limiting membrane and is not found in the lamellar body cont ents. Most multivesicular bodies of type II cells were also labeled, a s were some small cytoplasmic vesicles. Golgi complex labeling and pla sma membrane labeling were weak. The appearance of lbm180 protein by i mmunofluorescence in fetal rat lung cryosections correlated with the b iogenesis of lamellar bodies. The lbm180 protein decreased with time i n type II cells cultured on plastic. The lbm180 protein is an integral membrane protein of lamellar bodies and was also found in the pancrea s and the pancreatic beta HC9 cell line but not in the rat brain, live r, kidney, stomach, or intestine. The present study provides evidence that the lbm180 protein is a lung lamellar body and/or multivesicular body membrane protein and that its antibody, MAb 3C9, will be a valuab le reagent in further investigations of the biogenesis and trafficking of type II cell organelles.