Neuronal Circuits Modulate Antigen Flow Through Lymph Nodes.

When pathogens and toxins breech the epithelial barrier, antigens are transported by the lymphatic system to lymph nodes. In previously immunized animals, antigens become trapped in the draining lymph nodes, but the underlying mechanism that controls antigen restriction is poorly understood. Here we describe the role of neurons in sensing and restricting antigen flow in lymph nodes. The antigen keyhole-limpet hemocyanin (KLH) injected into the mouse hind paw flows from the popliteal lymph node to the sciatic lymph node, continuing through the upper lymphatics to reach the systemic circulation. Re-exposure to KLH in previously immunized mice leads to decreased flow from the popliteal to the sciatic lymph node as compared with naïve mice. Administering bupivacaine into the lymph node region restores antigen flow in immunized animals. In contrast, neural activation using magnetic stimulation significantly decreases antigen trafficking in naïve animals as compared with sham controls. Ablating Na1.8 + sensory neurons significantly reduces antigen restriction in immunized mice. Genetic deletion of FcγRI/FcεRI also reverses the antigen restriction. Colocalization of PGP9.5-expressing neurons, FcγRI receptors and labeled antigen occurs at the antigen challenge site. Together, these studies reveal that neuronal circuits modulate antigen trafficking through a pathway that requires Na1.8 and FcγR.