The image is superimposed video time-lapse images showing three time periods where movement of lymphocytes, a type of immune cell, from the medulla of the lymph node into the lymphatic sinus is being imaged in life. In the upper panel, the S1P1 agonist arrests lymphocyte movement. Intravenous injection of the S1P1 antagonist W146 reverses the inhibition of lymphocyte egress. The stromal barrier inhibiting lymphocyte movement from the medulla into the sinus is loosened and lymphocyte trafficking is restored.