Comparative evaluation of in vitro human macrophage models for mycobacterial infection study

Macrophages are phagocytic cells that play a key role maintaining the homeostasis of many tissues. Their function is essential for controlling and eradicating infecting mycobacteria. Human monocytic cell lines such as THP-1 and U937 have provided interesting insights into how mycobacteria subvert the host cell response. However, immortalized cell lines could bring some disadvantages. Here we compare the response of THP-1 and U937 cell lines with human monocyte-derived macrophages (hMDMs) to determine functional differences during infection with different mycobacterial phenotypes (virulent Mycobacterium tuberculosis H37Rv and Mycobacterium bovis, and attenuated M. bovis BCG). The findings of this study indicate that the U937 cell line displays a significantly lower phagocytic capacity than hMDMs and THP-1 macrophages, regardless of the mycobacterial strain. In all cell models, interferon-γ activation leads to up-regulation of interleukin-12 and nitrite production. However, the phorbol 12-myristate 13-acetate (PMA)-induced differentiation of U937 and THP-1 cell lines induces a significant tumor necrosis factor-α production in resting macrophages. However, this state of activation has no effect on the control of intracellular growth of mycobacteria. Moreover, U937 cells show more discrepancies with hMDM than THP-1. This study demonstrates that THP-1 macrophages exhibit closer functional similarities to hMDMs in response to mycobacterial infection, regardless of the strain.