CCL19 and lymphopenia: We hypothesized that this decrease in the cell surface expression of the receptor was a consequence, rather than the cause of the observed lymphopenia in the irradiated lymph nodes, similar to lymphodepleted lymph nodes in mice carrying the paucity of lymph node T cells (plt) mutation, which results in a lack of expression of the homeostatic chemokines CCL19 and CCL2145,46.