Capacity of Mycobacterium avium isolates to grow well or poorly in murine macrophages resides in their ability to induce secretion of tumor necrosis factor.

The results of this study show that clinical isolates of Mycobacterium avium fall into two categories in terms of their capacity to grow within murine bone marrow-derived macrophage cultures: those that grow progressively and those that are incapable of growing within such cells. Members of the first category were invariably of the smooth-transparent colonial type, while most of the second were of the smooth-doomed type. In addition, this paper shows that although all isolates induced tumor necrosis factor (TNF) secretion by host cells to some extent, this production was always delayed in isolates that subsequently grew well in the host cells. This observation, coupled with the demonstration that the growth of the latter isolates was inhibited by the exogenous addition of TNF, leads us to hypothesize that the ability of a given isolate to somehow avoid host macrophage TNF production early during the course of the infection is a key factor in the pathogenesis of the disease.