metabolism Sphingolipidoses are a group of diseases that are associated with the accumulation of sphingolipids which have not been degraded correctly, normally due to a defect in a glycoside hydrolase enzyme. Sphingolipidoses are typically inherited, and their effects depend on which enzyme is affected, and the degree of impairment. One notable example is Niemann–Pick disease which can cause pain and damage to neural networks, and is usually fatal in early infancy. Function Cell–cell interactions The main function of glycolipids in the body is to serve as recognition sites for cell–cell interactions. The saccharide of the glycolipid will bind to a specific complementary carbohydrate or to a lectin (carbohydrate-binding protein), of a neighboring cell. The interaction of these cell surface markers is the basis of cell recognitions, and initiates cellular responses that contribute to activities such as regulation, growth, and apoptosis. Immune responses An example of how glycolipids function within the body is the interaction between leukocytes and endothelial cells during inflammation. Selectins, a class of lectins found on the surface of leukocytes and endothelial cells bind to the carbohydrates attached to glycolipids to initiate the immune response. This binding causes leukocytes to leave circulation and congregate near the site of inflammation. This is the initial binding mechanism, which is followed by the expression of integrins which form stronger bonds and allow leukocytes to migrate toward the site of inflammation. Glycolipids are also responsible for other responses, notably the recognition of host cells by viruses. Blood types Blood types are an example of how glycolipids on cell membranes mediate cell interactions with the surrounding environment. The four main human blood types (A, B, AB, O) are determined by the oligosaccharide attached to a specific glycolipid on the surface of red blood cells, which acts as an antigen. The unmodified antigen, called the H antigen, is the characteristic of type O, and is present on red blood cells of all blood types. Blood type A has an N-acetylgalactosamine added as the main determining structure, type B has a galactose, and type AB has all three of these antigens. Antigens which are not present in an individual's blood will cause antibodies to be produced, which will bind to the foreign glycolipids. For this reason, people with blood type AB can receive transfusions from all blood types (the universal acceptor), and people with blood type O can act as donors to all blood types