Enzymes in tuberculous lesions hydrolyzing protein, hyaluronic acid and chondroitin sulfate: a study of isolated macrophages and developing and healing rabbit BCG lesions with substrate film techniques; the shift of enzyme pH optima towards neutrality in 'intact' cells and tissues

By substrate film techniques, enzymes hydrolyzing protein, hyaluronic acid and chondroitin sulfate were evaluated in glycogen induced peritoneal polymorphonuclear (PMN), oil induced peritoneal mononuclear phagocytes (MN) and pulmonary alveolar macrophages (AM) obtained from rabbits. PMN showed the absence or low levels of these enzymes, MN showed moderate levels and AM showed high levels. The pH optimum for whole AM was about 5 when assayed on proteins in substrate films, but the pH optimum for homogenized AM was between 3 and 4 when assayed on proteins in solution. AM homogenates (and purified rabbit lung cathepsin D) retained the pH optimum of 3 to 4 when placed on protein substrate films. Similarly, the pH optimum for whole AM was between 7 and 8 when assayed on hyaluronic acid (and chondroitin sulfate) in substrate films, but the pH optimum was 4 when extracts of AM were assayed on hyaluronic acid in solution. For sections of BCG lesions on the substrate films, the pH optima resembled AM. Thus hydrolytic enzymes in 'intact' cells and tissues apparently have a higher pH optimum than enzymes in tissue homogenates, possibly due to the presence of activators or inhibitors or other types of interacting molecules. Substrate film techniques were also applied to frozen sections of rabbit dermal and pulmonary BCG lesions in various stages of development and healing. Proteinase, hyaluronidase and chondroitinase were most active in lesions after delayed hypersensitivity and caseation occurred. Apparently, the hypersensitivity process as well as the ingestion of necrotic material stimulated macrophages to increase their levels of these hydrolases. Enzymes hydrolysing protein, hyaluronic acid, chondroitin sulfate (and DNA and RNA described previously), frequently remain active after the macrophage has died and become part of the caseous center of the tubercle. These enzymes probably cause the caseous material to liquefy. Liquefaction enables the tubercle bacillus to grow in tremendous numbers extracellularly and perpetuate the disease in mankind.