UCSF

Apoptosis is critical for the elimination of activated lymphocytes after viral infection. Proapoptotic factor Bim (Bcl2l11) controls T lymphocyte contraction and the formation of memory T cells after infection. Natural killer (NK) cells also undergo antigen-driven expansion to become long-lived memory cells after mouse cytomegalovirus (MCMV) infection; therefore, we examined the role of Bim in regulating the MCMV-driven memory NK cell pool. Despite responding similarly early after infection, Bcl2l11(-/-) Ly49H(+) NK cells show impaired contraction and significantly outnumber wild-type (WT) cells after the expansion phase. The inability to reduce the effector pool leads to a larger Bcl2l11(-/-) NK memory subset, which displays a less mature phenotype (CD11b(lo), CD27(+)) and lower levels of NK cell memory-associated markers KLRG1 and Ly6C. Bcl2l11(-/-) memory NK cells demonstrate a reduced response to m157-mediated stimulation and do not protect as effectively as WT memory NK cells in an MCMV challenge model. Thus, Bim-mediated apoptosis drives selective contraction of effector NK cells to generate a pool of mature, MCMV-specific memory cells.