Prostaglandin E2 is the major prostaglandin produced by macrophage cells, which is derived from 20-carbon polyunsaturated fatty acids synthesized in a wide range of tissue types. In humans, PGE2 is a well-known pro-inflammatory mediator involved in diverse functions, including heat releasing, strengthening the permeability of blood vessel, accelerating the release of lysozyme, interferon, erythrogenin, colony stimulating factor and accelerating chemotaxis of leucocyte et al. . The key regulatory enzyme of PGE2 biosynthesis is cyclooxygenase, and cyclooxygenase-2 is the inducible form of this enzyme and mediates many of the inflammatory and inducible effects. It is therefore worth screening the effect of foods on COX-2 expression and PGE2 formation which can provide useful information on inflammatory conditions .
Nitric oxide is known to play an important role in the maintenance of tissue homeostasis. NO is produced by nitric oxide synthase, and the inducible isoform (iNOS) is known to be implicated under several pathological conditions including inflammation. NO produced by iNOS kills infectious pathogens, but Overproduction of NO result damage to tissues and eventually destruction of tissue homeostasis . Thus, the iNOS expression and NO production might be a good target for inflammatory research.
For 2,000 years, people in Chinese society have believed that certain foods are either 'heating' (or 'fire increasing') or 'cooling' (or 'fire reducing') in the body when eaten . According to traditional Chinese medicine, symptoms for the diagnosis of a 'heating' disease state include dry mouth, a bitter taste sensation, throat swelling and sore, boil of the lips and a rough yellow tongue, flushing and even fever .
In contrast, disease states in which the patient is thirsty but is not willing to drink, and has pallor, diarrhea, a large amount of diluted urine, a smooth white tongue and a slow pulse are diagnosed as 'cooling'. Weakness, tiredness, cold body temperature and shivering are also reported to be 'cooling' conditions .
In agreement with the Chinese belief of yin and yang, health is thought to result from a proper balance of 'heating' and 'cooling' foods and activities, and illness is treated with foods or medicines with properties opposite to those of the disease .
Most of foods are neutral. Moreover, foods can change categories as a result of different cooking methods . For example, fried peanuts are typical 'heating' foods, but boiled and steamed peanuts are not. Fried foods and meat cooked in black sesame oil with ginger are also good examples of 'heating' foods produced by a cooking method.
Most 'cooling' foods are of plant origin, especially fruits and vegetables. Many, but not all, of the 'cooling' fruits and vegetables have a high water content, e.g. watermelon and radish, and excretion of a large volume of diluted urine is considered one of the 'cooling' conditions. However, not all vegetables are 'cooling', many are neutral, and a few fruits, such as litchi, longan, and durian, are considered to be 'heating'.
Although there has been speculation on the significance and rationale of the 'hot/cold' food belief from a social science aspect , an empirical rational basis has not been reported. A chemical feature common to 'hot' or 'cold' foods cannot be ruled out simply based on the nutrient composition, implying that some components with special functions may be involved. On the other hand, the class of body regulator that is targeted by 'hot' or 'cold' foods and mediates the diverse 'hot/cold' syndrome must be one that has a wide range of functions or can trigger diverse physiological changes in the body.
Since the extreme case of a 'heating' condition resembles inflammation in certain ways, PGE2 and NO could be used as the research target for 'heating' foods, feeding mice a diet containing frying oil tended to increase PGE2 production by peritoneal macrophages and fried foods are very common 'heating' foods [8, 11], the effect of some typical 'heating' and 'cooling' foods on PGE2 production was tested using a murine macrophage cell line, J774, as an in vitro model . For example, Lii CK found the ethanol extract of bitter gourd showed the greatest reduction of PGE2 production in LPS-stimulated RAW 264.7 macrophage cells  and Wu WH et al. identified short and medium chain fatty acids are the major activity ingredient in bitter gourd, in which capric acid exhibited the highest effect .
Litchi chinensis Sonn (Sapindaceae) is an evergreen shrub or tree, as an improtant economic fruit, is widespread in the south of China (Gontier et al., 2000). As describe above, Litchi is typical a 'heating' fruits which causes inflammatory conditions  and there are no reports of specific ingredients found in litchi fruit which take the effects on PGE2 or NO production. Therefore, the objective of this study was carried out for the first time to isolate the possible compounds in litchi fruit and to determine their inflammatory effects on PGE2 and NO production in J774 murine macrophage cells as well as the related gene expression.