The human macrophage cell line U937 as an in vitro model for selective evaluation of mycobacterial antigen-specific cytotoxic T-cell function

Despite strong evidence for CD8(+) T-cell function in murine mycobacterial infections, their corresponding role in human tuberculosis has proven more difficult to demonstrate. We have evaluated the human macrophage (M phi) ce ll line U937 as an in vitro model for human leucocyte antigen (HLA) class I -restricted presentation of mycobacterial antigens, as HLA class I is const itutively expressed at high levels by U937 cells in the absence of detectab le HLA class II or CD1 molecules. U937 cells were evaluated for their abili ty to phagocytose Mycobacterium tuberculosis and for their ability to prese nt mycobacterial antigens to human HLA class I-matched cytotoxic T lymphocy tes (CTLs). Differentiated U937 cells were capable of efficient phagocytosi s of M. tuberculosis but did not generate a subsequent respiratory burst re sponse, and were permissive for intracellular growth of both bacillus Calme tte-Guerin (BCG) and the virulent M. tuberculosis H37Rv strain. CTL activit y was restricted to live mycobacterial organisms and was shown to be mediat ed by M. tuberculosis-specific, HLA class I-matched, purified CD8+ CTL line s and CD8(+) T-cell clones. Furthermore, M. tuberculosis-infected U937 targ ets were more rapidly and strongly lysed by CD8(+) CTLs than were infected autologous M phi. Finally, M. tuberculosis-infected U937 cells simultaneous ly provided a sensitive indicator for detection of mycobacterial-specific, HLA-unrestricted gamma delta (+) CTL activity.