T lymphocytes circulate between the blood, tissues, and lymph. These T cells carry out immune functions, using the C-C chemokine receptor 7 (CCR7) and its cognate ligands, CCL19 and CCL21, to enter and travel through the lymph nodes. Distinct roles for each ligand in regulating T lymphocyte trafficking have remained elusive. We report that in the human T cell line HuT78 and in primary murine T lymphocytes, signaling from CCR7/CCL19 leads to increased expression and phosphorylation of extracellular signal-regulated kinase 5 (ERK5) within eight hours of stimulation. Within 48–72 h we observed peak levels of endothelial differentiation gene 1 (EDG-1), which mediates the egress of T lymphocytes from lymph nodes. The increased expression of EDG-1 was preceded by up-regulation of its transcription factor, Krüppel-like factor 2 (KLF-2). To determine the cellular effect of disrupting ERK5 signaling from CCR7, we examined the migration of ERK5flox/flox/Lck-Cre murine T cells to EDG-1 ligands. While CCL19-stimulated ERK5flox/flox naïve T cells showed increased migration to EDG-1 ligands at 48 h, the migration of ERK5flox/flox/Lck-Cre T cells remained at a basal level. Accordingly, we define a novel signaling pathway that controls EDG-1 up-regulation following stimulation of T cells by CCR7/CCL19. This is the first report to link the two signaling events that control migration through the lymph nodes: CCR7 mediates entry into the lymph nodes and EDG-1 signaling controls their subsequent exit.

Functional loss of C-C chemokine receptor 7 (CCR7) and its ligands, CCL19 and CCL21, has been linked to development of autoimmune diseases. Therefore, we hypothesized that CCR7 antagonists could be used to promote an immune response that could be measured by tittering antibodies produced in animals injected with test antigens. To test this hypothesis we injected C57BL/6 mice on day 0 and boosted on day 20 with dinitrophenol (DNP)-Keyhole Limpet Hemocyanin (KLH) with a CCL19 antagonist, 8-83, or with the agonist solvent as a control. Similar to the CCR7-/- mouse, which has significantly elevated levels of IgG1, IgG2a, IgG2b and IgG3 by day 30, the animals treated with 8-83 generated significantly higher levels of IgG1 and IgG2a, than animals injected with the DNP-KLH/solvent alone. Previous studies by our laboratory have shown that CCL19 signals through ERK5. To determine if loss of signaling through ERK induced a similar increase in the levels of IgGs, we injected ERK5flox/flox control mice or ERK5flox/floxLck-Cre mice with DNP-KLH. Similar to animals treated with 8-83, the ERK5flox/flox Lck-Cre mice produced significantly higher levels of IgG1, IgG2a and IgG3 than control mice. From these results we conclude that CCR7/CCL19 signals through ERK5 to control the levels of antibodies made. Recent studies demonstrating a role for CCR7 in controlling the localization of regulatory T cells may provide insight into immune cells that are regulate observed increase in antibody titers.