The in vivo role of murine natural killer cells in the development of B cell lineage in bone marrow.

Physiological functions of natural killer (NK) cells in the development of bone marrow cells into the cells expressing B cell characteristics were examined in recipient mice expressing different allotype immunoglobulins (Ig) or in mutants defective in lipopolysaccharide (LPS) response. When the irradiated BALB/c nude mice (Igha) were injected with bone marrow cells of C57BL/6N (B6,Ighb), the level of donor-type serum Ig (Ighb) was about 10 fold higher in the mice with NK activity depleted by injecting anti-asialo GM1 compared to that of mice with the normal NK activity on day 21 after bone marrow transplantation. In the irradiated C3H/HeJ (low responder) which received bone marrow cells of C3H/HeN (high responder), augmentation of polyclonal antibody response and of the cell proliferation with LPS was demonstrated in the NK depleted mice. However, the difference in the level of donor-type Ig or LPS response between the NK-depleted and intact mice disappeared in 3 to 4 weeks. In normal mice without irradiation and marrow cell transplantation, NK cell elimination from spleen cells did not give rise to distinctly enhanced responses to in vitro LPS stimulation, whereas mice with augmented NK activity by poly I:C demonstrated a suppressed response to LPS when the mice were immunized with LPS. Collectively, these observations suggested that NK cells are involved in the suppressive regulation of developing B cell lineage as well as activated B cells in vivo.