Lipoarabinomannan from Mycobacterium smegmatis Stimulates an Inflammatory Response in RAW 264.7 Murine Macrophages

Macrophages are a key leukocyte in defense against Mycobacterium tuberculosis infection. The precise mechanism by which M. tuberculosis evades host macrophage defenses remains unknown, so understanding how macrophages interact with cell wall components of mycobacteria is critical. Lipoarabinomannan (LAM) is a glycolipid Toll-like receptor-2 (TLR-2) ligand found on the cell wall of mycobacteria, and is thought to contribute to the cell wall structural integrity. When LAM binds to TLR on host leukocytes, this activates cellular responses and phagocytosis by host macrophages. Nitric oxide production can be used as a measure of inflammatory response and can be evaluated via nitrite response measured using the Greiss reaction. The purpose of this research was to evaluate the optimal dose of LAM to elicit a nitric oxide in RAW 264.7 murine macrophages. Experimental concentrations of LAM were 10 ng/mL, 100 ng/mL, and 1000 ng/mL, 2000 ng/mL, 3000 ng/mL, and 5000 ng/mL, and were compared to a positive control of 100 ng/mL lipopolysaccharide (LPS) from Escherichia coli (O55:B5). LAM from M. smegmatis exhibited a dose-response effect in RAW 264.7 macrophages. The highest LAM dose of 5000 ng/mL stimulated the greatest production of nitric oxide inflammatory mediator