Lipids

the class of lipid that are involve in the inflammatory response is call the eicosanoid. the eicosanoid is a 20 carbon chain fatty acid. I think there are 4 members which belong to this class of lipid:
the prostaglandins, prostacyclins, thromboxanes and leukotrienes.

when our body are encountering allergen, just like the police force, there are few objective that need to be cover, firstly, you have to alert the host that there are allergen around, and the host should avoid it. Secondly, the allergen should be isolated at the site so that it will not travel to other part of the body. Finally, "killer" should be alert so it will remove the threat.

At this part, i am a bit rusty with the chemical physiology (i did it 20 years ago), I think what happen is: macrophage discovered the allergen and started the "eating" process, it will eat until death and release a sac of chemical mediator to alert the surrounding and trigger an inflammatory response. these chemical messengers includes PG and IL. The PG will cause pain and alert the host that they are being attack by allergen, togenther with Il will cause swelling, i.e. slow down the blood flow and isolated the allergen, part of the IL will alert other white cell to the site and repeat the process.