Lysosomal acid esterase: activity and isoenzymes in separated normal human blood cells.

The striking difference in the cytochemical pattern of acid esterase between blood monocytes and T lymphocytes initiated the present study to determine whether or not the cytochemical difference is related to a cell-specific polymorphism of the isoenzymes. Enzyme assays and isoelectric focusing were performed using detergent-treated lysosomes from viable monocytes, granulocytes. T lymphocytes, platelets. and erythrocytes isolated from peripheral blood. B lymphocytes were separated from tonsils. Thymocytes were obtained from thymus glands excised during cardiac surgery. Except for monocytes, all cell suspensions showed a purity of more than 98%. The mean enzyme activity in monocytes amounted to 39 mU/107 cells. This value was 7 times higher than the activity level of lymphocytes. which showed values of 5.5 mU for io B lymphocytes. 5.3 mU for iO T lymphocytes. and 8.1 mU for i07 thymocytes. Granulocytes exhibited the lowest enzyme activity. The isoelectric focusing pattern of monocytes disclosed 4 isoenzymes. with the anodic one accounting for more than 85% of the total activity. T lymphocytes had 1 3-1 6 bands distributed in 3 complexes between pH 7.9 and 4.5. Thymocytes displayed a similar pattern. with only 1 1 bands. B lymphocytes showed 7 isoenzymes between pH 6.4 and 5.5. Platelets revealed 10 bands (pH 7.5-5.8), and erythrocytes. 5 ill-defined bands (pH 5.6-4.9). These data illustrate the diversity of the lysosomal acid esterase isoenzymes of the different types of blood cells. The characteristic isoenzyme pattern of acid esterase in T lymphocytes and monocytes is well in line with the cytochemical staining pattern and indicates the existence of cell-specific enzyme variants.