SUBSTRATE-SPECIFIC PROTEASES (BLT-ESTERASE) ARE LOCALIZED PREDOMINANTLY IN THE NATURAL-KILLER-CELLS OF UNPRIMED MICE

In leukocytes isolated from unprimed mice, the levels of extractable N alpha-Cbz-Lys-thiobenzylesteresterase (BLT-esterase) closely correlate d with the number of natural killer (NK) cells. The spleens of mice th at exhibit severe combined immunodeficiency (SCID) contained much high er levels of this enzyme than other mouse strains. Treatments that res ulted in a local accumulation of NK cells (as assessed by lytic activi ty) produced a concomitant increase in BLT-esterase activity. However, short-term in vitro treatment of spleen cells with interferon (IFN)-a lpha/beta indicated that BLT-esterase levels correlated more closely w ith absolute numbers of NK cells than with their lytic capacity. There was a very good correlation between the numbers of cells bearing the NK phenotype (NK-1.1+) and BLT-esterase levels. Cells positively sorte d using the NK-specific antibodies NK-1.1 and LGL-1 had high enzymatic activity. The BLT-esterase levels were high in both the NK-1.1+/LGL-1 - and NK-1.1+/LGL-1+ subsets. Highly purified CD4+ and CD8+ T cells an d sIg+ B cells demonstrated negligible enzyme, as did populations of c ells highly enriched for macrophages or neutrophils. However, it shoul d be stressed that the inbred mice used on this study have been mainta ined in a pathogen-free facility. It would be anticipated that mice ma intained under less stringent conditions could exhibit appreciable lev els of BLT-esterase activity in their T cells. Nonetheless, BLT-estera se is present at high levels in NK cells and cannot be regarded as a T cell-specific enzyme.