Antigen localization in lymphopenic states. II. Further studies on whole body x-irradiation

Abstract

The gross and microscopic distribution of ¹²⁵I polymerized flagellin from Salmonella adelaide was studied in adult rats at various times following 800 r whole body X-irradiation. Injections of radioactive antigen were made in both hind footpads, and the popliteal lymph nodes were excised for autoradiographic study 1 day later. This dose of irradiation caused a progressive decline in the ability of lymphoid follicles of popliteal nodes to capture and retain antigen. Irradiation had no detectable effect upon antigen uptake by whole lymph nodes or upon the number of grains overlying the phagocytic cells of the medullary sinuses of popliteal nodes.

Various substances capable of restoring follicular antigen uptake in the irradiated rat were studied by means of injecting the test substance into one hind footpad 1 hour prior to the injection of antigen into both feet. The distribution of antigen in each popliteal node was compared, each animal thus acting as its own control. It was found that 0.01 ml of specific anti-flagellar immune serum, or 0.25 ml of normal adult rat serum significantly improved follicular antigen uptake when tested ten days after irradiation. Foetal calf serum, homologous lymphocytes, and the media from pooled concentrated lymphocyte cultures were without demonstrable effects when given by regional injection. Shielding of the popliteal nodes at the time of irradiation improved follicular antigen uptake, whereas shielding of the femoral bone marrow and appendix was ineffective. No agent found capable of improving follicular antigen capture in the irradiated rat significantly altered footpad retention of antigen, whole organ counts of the popliteal nodes, or antigen localization in the phagocytic cells of the lymph node medulla.

The results favour the interpretation that the follicular antigen trapping mechanism is extremely sensitive to changes in levels of opsonins; that substances present in normal adult rat serum act as `follicular opsonins'; that these substances decline exponentially following irradiation; and that these substances are secreted by small lymphocytes or their progeny.