Limitations of safranin 'O' staining in proteoglycan-depleted cartilage demonstrated with monoclonal antibodies

The intensity of safranin 'O' staining is directly proportional to the proteoglycan content in normal cartilage. Safranin 'O' has thus been used to demonstrate any changes that occur in articular disease. In this study, staining patterns obtained using monoclonal antibodies against the major components of cartilage proteoglycan chondroitin sulphate (anti CS) and keratan sulphate (anti KS), have been compared with those obtained with safranin 'O' staining, in both normal and arthritic tissues. In cartilage where safranin 'O' staining was not detectable, the monoclonal antibodies revealed the presence of both keratan and chondroitin sulphate. Thus, safranin 'O' is not a sensitive indicator of proteoglycan content in diseases where glycosaminoglaycan loss from cartilage has been severe.