| The immune system is tightly regulated in order to balance host protection and autoimmunity. Two G-protein coupled receptors that assist in immune regulation and are expressed in both thymocytes and peripheral T cells are termed vasoactive intestinal peptide receptor 1 (VPAC1) and VPAC2. Both receptors have a common ligand, vasoactive intestinal peptide (VIP), which evokes intracellular signaling to modulate numerous functions including proliferation and trafficking. However, the expression profile and regulatory mechanisms of these receptors have not been mapped throughout thymocyte development or during the T cell immune response. Gaining knowledge of VIP receptor's T cell expression profile will be critical in understanding how this signaling axis mediates immune protection. We hypothesized that VPAC1:VPAC2 expression ratios would be adjusted during high bursts of proliferation in thymocyte development stages and immune response phases. We demonstrated that the VPAC1:VPAC2 ratio was low during early double negative (DN) 1, 2, and 3 thymocyte development stages. At latter stages of development (DN4), there was a receptor switch to a high VPAC1:VPAC2 ratio, which remained into mature, peripheral T cells. During an immune T cell response, we demonstrated that VPAC2 expression was undetected, while VPAC1 expression was downregulated 163-fold during expansion, was restored during contraction and into the memory phase. After re-challenge, VPAC1 was downregulated five-fold in expanding memory T cells and remained at this decreased expression level in secondary memory cells. We also explored the signaling pathway regulation controlling VPAC1 expression in activated T cells and discovered that osmotic stress alters VPAC1 and VPAC2 expression in T cells. Regarding the signaling mechanism, after T cell activation, VPAC1 downregulation was through a Fyn/Lck3 → Zap70 → JNK signaling pathway. With respect to osmolarity, VPAC1 was indirectly proportional, while VPAC2 was directly proportional to osmolarity changes. Overall, VPAC1 and 2 receptors function in directing progression of T cells through thymocyte development and T cell homeostasis. Additionally, we determined that VPAC1 regulation in T cells is controlled by T cell receptor engagement and signaling through JNK, as well as changes in osmolarity. These findings suggest strong roles for these two GPCRs in maintaining a tightly regulated immune system network. |
