Studies on the effects of marijuana smoking have evolved into the discovery and description of the endocannabinoid system. To date, this system is composed of two receptors, CB1 and CB2, and endogenous ligands including anandamide, 2-arachidonoyl glycerol, and others. CB1 receptors and ligands are found in the brain as well as immune and other peripheral tissues. Conversely, CB2 receptors and ligands are found primarily in the periphery, especially in immune cells. Cannabinoid receptors are G protein-coupled receptors, and they have been linked to signaling pathways and gene activities in common with this receptor family. In addition, cannabinoids have been shown to modulate a variety of immune cell functions in humans and animals and more recently, have been shown to modulate T helper cell development, chemotaxis, and tumor development. Many of these drug effects occur through cannabinoid receptor signaling mechanisms and the modulation of cytokines and other gene products. It appears the immunocannabinoid system is involved in regulating the brain-immune axis and might be exploited in future therapies for chronic diseases and immune deficiency.

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Legionella pneumophila is a facultative intracellular bacterium which readily grows in cultures of guinea pig and human mononuclear phagocytes. In this report, we demonstrate that the Legionella sp. also grows in thioglycolate-elicited macrophages obtained from A/J mice but not in cells from other mouse strains tested, such as BDF1, DBA/2, C3H/HeN, C57BL/6, and BALB/c. Growth of Listeria monocytogenes and interleukin-1 production in A/J mice were similar to their growth and production in other strains tested, and the growth of Staphylococcus epidermidis was restricted by A/J macrophages. This finding suggests that although A/J macrophages share functional capabilities with cells from other mouse strains, they differ in growth restriction capacity for the Legionella sp. Resident macrophages were less permissive than were thioglycolate-elicited cells in that resident cells from A/J mice failed to support the growth of Legionella pneumophila. Also, resident cells from BDF1 mice rapidly eliminated the bacteria, rather than merely restricting growth. This finding was also observed in in vivo studies in which thioglycolate pretreatment of mice resulted in the enhanced recovery of viable bacteria from the peritoneal cavity of mice infected intraperitoneally. Higher numbers of bacteria were obtained from A/J mice and, in addition, this strain was more susceptible to the lethal effects of LegioneUa infection. These data suggest that, as with other intracellular bacteria, macrophages may serve a pivotal role in the early stages of Legionella infection and further suggest that the A/J mouse represents a useful animal model for the study of Legionella infection and immunity.

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