APPARENT KILLING OF MYCOBACTERIUM-TUBERCULOSIS BY CYTOKINE-ACTIVATED HUMAN MONOCYTES CAN BE AN ARTIFACT OF A CYTOTOXIC EFFECT ON THE MONOCYTES

A protocol using combined exposure to interferon-gamma (IFN-gamma), ca lcitriol and tumour necrosis factor-alpha (TNF-alpha) has been reporte d to activate human monocytes in vitro to kill Mycobacterium tuberculo sis. We have attempted to repeat the findings in two laboratories, wit h negative results; treated cells were no different from untreated cel ls in this respect. However, the treated cells were more sensitive to a toxic effect of the bacteria. We suggest that the reported dramatic mycobacterial killing may have been an illusory consequence of the tox icity leading to cell lysis and loss of the liberated bacteria from th e assay.