Evidence of antibody production in the rat cervical lymph nodes after antigen administration into the cerebrospinal fluid

We previously showed histologically that, in the rat, the cerebrospinal fluid drains from the subarachnoid space along the olfactory nerves to the nasal lymphatics and empties into the superficial and deep cervical lymph nodes. The present study was performed to investigate whether these lymph nodes play a role in the immune response of the central nervous system. For this purpose, keyhole limpet hemocyanin conjugated with fluorescein isothiocyanate (KLH-FITC) was administered into the subarachnoid space of the rat brain, and the time-kinetics and location of FITC and anti-FITC antibody forming cells in the cervical lymph nodes were studied histologically and immunohistochemically. FITC fluorescence was detected in superficial and deep cervical lymph nodes as well as the subarachnoid space and the nasal mucosa 2 h after FITC-KLH injection into the subarachnoid space. The specific antibody-forming cells first appeared in both the superficial and deep cervical lymph nodes on the 4th day after antigen administration although the reaction was more intense in the deep than in the superficial cervical lymph nodes. These cells were located in the medullary cords of the cervical lymph nodes. The number of antibody forming cells increased thereafter, reached a peak around the day 6, and then declined on day 10. These findings indicate that antigens introduced in the cerebrospinal fluid are drained into the cervical lymph nodes through the nasal lymphatics and initiate the antigen-specific immune response there. Thus, the cervical lymph nodes probably act as a monitoring site for cerebrospinal fluid and play a major role in the central nervous system immune response.