Alternative Medicine Review 2008 (Jun); 13 (2): 165–167 ~ FULL TEXT
Boswellia serrata (frankincense) is a moderate-to-large branching tree (growing to a height of 12 feet) found in India, Northern Africa, and the Middle East. Strips of Boswellia bark are peeled away, yielding a gummy oleo-resin. Extracts of this gummy exudate have been traditionally used in the Ayurvedic system of medicine as an anti-arthritic, astringent, stimulant, expectorant, and antiseptic.
Boswellia contains oils, terpenoids, sugars, and volatile oils. Up to 16 percent of the resin is essential oil, the majority being alpha-thujene and p-cymene. Four pentacyclic triterpene acids are also present, with beta-boswellic acid being the major constituent.
Mechanisms of Action
Animal studies performed in India show ingestion of a defatted alcoholic extract of Boswellia decreased polymorphonuclear leukocyte infiltration and migration, decreased primary antibody synthesis, [1,2] and almost totally inhibited the classical complement pathway.  In an in vitro study of the effects of beta-boswellic acid on the complement system, the extract demonstrated a marked inhibitory effect on both the classical and alternate complement pathways.  An investigation of Boswellia's analgesic and psychopharmacological effects noted marked sedative and analgesic effects in animal models. 
In vitro testing reveals boswellic acids, isolated from the gum resin of Boswellia, in a dose-dependent manner block the synthesis of proinflammatory 5-lipoxygenase products, including 5-hydroxyeicosatetraenoic acid (5-HETE) and leukotriene B4 (LTB4),  which cause bronchoconstriction, chemotaxis, and increased vascular permeability. 
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