Lymph node localization and whole body distribution of radioiodinated encephalitogenic polypeptide in guinea-pigs.

A bovine encephalitogenic polypeptide (BEP) labelled with radioiodide retained its capacity to induce experimental encephalomyelitis (EAE). Guinea-pigs were injected with I BEP in Freund's complete adjuvant (FCA), to study changes in the architecture and the distribution of radioactivity in draining lymph nodes, and the amount of radioactivity in various organs. After injection of BEP in FCA the lymph node rapidly enlarged. Within 48 hr there was depletion of lymphocytes, the enlarging lymphoid follicles had become confluent and there was proliferation of large `epithelioid' cells throughout the node. At 5 days the lymph node architecture was disorganized and lymph follicles with germinal centres could not be recognized; similar but less pronounced changes were present in regional nodes. By contrast, after injection of flagellin in FCA, there were numerous lymphocytes, plasmablasts and pyroninophilic cells, germinal centres were prominent, and the architecture was preserved. From 0·5 to 0·8% of the total injected radioactivity was concentrated in the popliteal lymph node 2–5 days after injection of I BEP in FCA. No radioactivity was concentrated in the node after injection of I BEP without FCA, and animals thus immunized did not develop encephalomyelitis. The popliteal lymph node was examined by autoradiography after injection of I BEP in FCA. At 24 hr radioactive encephalitogen associated with droplets of adjuvant was present mainly in the peripheral sinus and at 48 hr encephalitogen–adjuvant droplets were deposited randomly throughout cortex and medulla. These droplets appeared to represent sites where lymphoid cells acquired their capacity for pathogenic reactivity with their target antigen in the central nervous system.