Enhanced growth of Legionella pneumophila in tetrahydrocannabinol-treated macrophages.

Legionella pneumophila is an opportunistic intracellular pathogen that infects macrophages, both in vivo and in vitro. Tetrahydrocannabinol is a major psychoactive component of marijuana and can affect the functional activity of macrophages. In the present study, it was found that the treatment of macrophage cultures from permissive A/J mice with THC enhanced the growth of Legionella in these cells. Legionella grew much better in macrophages treated with low doses of THC, which caused no alteration in the number or viability of macrophages, as compared with growth in untreated cells. Furthermore, lipopolysaccharide-treated A/J mouse macrophages restricted the growth of Legionella, but this growth restriction was overcome by the addition of THC to LPS-treated macrophage cultures after infection. Thus, it is apparent that THC has the ability to enhance the growth of the intracellular opportunistic pathogen Legionella that grows in A/J mouse macrophages.