The role of the lymphoid system in the regulation of the blood glucose level.

Recent findings have led to a new hypothesis in which it is proposed that the immune system plays a role in regulating the increase in blood glucose levels after a meal. The relevant findings are: (1) the primary lymphoid tissue, the lymph nodes are mostly present within adipose tissue depots throughout the body (there are at least 12 such depots and about 10 (12) lymphocytes, 99% of which are present in lymph nodes); (2) lymphocytes and other immune cells utilize glucose at a high rate but almost all of it is converted to lactate which accumulates in the cells prior to release; (3) glutamine, some of which is synthesized in muscle from glucose, is utilized at a high rate by immune cells, the end-product of which is mainly aspartate, which also accumulates in the cells prior to release; and (4) finally, there is a common blood supply to the lymph node and the adipose tissue depot and the blood flow through the depot and hence the node is increased after a meal. It is proposed that, after a meal, some of the absorbed glucose is taken up from the blood by the lymphocytes and converted to lactate and glutamine is converted to aspartate. These are released slowly into the blood from where they are removed and converted to glycogen by the liver. Hence the immune cells provide a temporary buffer for glucose in the form of lactate and aspartate and, in this way, restrict the rise in blood glucose during and after a meal.