Different Toll-like receptor agonists induce distinct macrophage responses

We previously reported that gram-negative bacterial Lipopolysaccharide (LPS ) activates cells via Toll-like receptor (TLR) 4, whereas the mycobacterial cell wall glycolipid Lipoarabinomannan (LAM) activates cells via TLR2, We also identified a secreted TLR2 agonist activity in shortterm culture filtr ates of Mycobacterium tuberculosis bacilli, termed soluble tuberculosis fac tor (STF). Here we show that STF contains mannosylated phosphatidylinositol (PIM) and that purified PIM possesses TLR2 agonist activity. Stimlulation of RAW 264.7 macrophages by LPS, LAM, STF, and PIM rapidly activated nuclea r factor (NF)-kappaB, activator protein-1 (AP-1), and mitogen-activated pro tein (MAP) kinases. These TLR agonists induced similar levels of NF-kappaB and AP-1 DNA-binding activity, as well as trans-activation function, Unexpe ctedly, these TLR agonists induced tumor necrosis factor alpha secretion, w hereas only LPS was capable of inducing interleukin-1 beta and nitric oxide secretion. Thus, different TLR proteins are still capable of activating di stinct cellular responses, in spite of their shared capacities to activate IVF-kappaB, AP-1, and MAP kinases.