Simultaneous development of cells with large granular lymphocyte (LGL) morphology and natural killer (NK) cell lytic activity after bone marrow (BM) transplantation in mice.

In the present study we investigated the development of natural killer (NK) cell lytic activity, and its correlation with the appearance of cells with large granular lymphocyte (LGL) morphology after bone marrow transplantation (BMT). NK activity was first found 7 days after bone marrow (BM) reconstitution, simultaneously with the appearance of the first LGLs. The number of LGLs, as well as the lytic activity, increased until Day 16 after BM reconstitution, after which they started to decrease, reaching the normal values of controls in 30 days. These early appearing LGLs differed somewhat from mature-type LGLs; they were larger, blast-like cells (found in the lower density fractions of Percoll gradient) and had a basophilic cytoplasma, in contrast to a pale cytoplasm in mature LGLs, but they expressed the asialo GM 1 (AGM 1) antigen like normal NK cells. Those NK cells that appeared first also tended to be lytically more effective than their mature counterparts. Taken together, these data suggest that the correlation between LGL morphology and NK lytic activity also holds true during the development of NK cells from their non-lytic precursors in the bone marrow.