Lipooligosaccharide (LOS) is a low-weight version of lipopolysaccharide present on the surfaces of most other Gram-negative bacteria. It is a sugar (saccharide) side chain attached to lipid A (thus "lipo-") in the outer membrane coating the cell wall of the bacteria. The root "oligo" refers to the fact that it is a few sugars shorter than the typical lipopolysaccharide. As an endotoxin, LOS provokes inflammation. The shedding of LOS by the bacteria is responsible for local injury in, for example, pelvic inflammatory disease. Although its main function is as an endotoxin, LOS may disguise itself with host sialic acid and block initiation of the complement cascade.