Recently, antibodies to the signal receptors on the blood vessels of the lower extremities have been discovered in the blood of some POTS patients. What role these antibodies play in the blunting of the autonomic nervous system signals remains uncertain. It has been postulated that these antibodies are in response to recent infections and may be responsible for the reduced sympathetic constriction of the veins of the lower extremities that occurs in POTS patients when standing. Reduced lower extremity venous constriction further encourages pooling of blood in the lower body and diminishes movement of blood upward.