The localization of non-microbial antigens in the draining lymph nodes of tolerant, normal and primed rabbits.

Soluble haemocyanin (HCy) or human serum albumin (HSA) labelled with I at 8 and 0·7 μc/μg, respectively, were injected into the footpads of rabbits in doses just sufficient to elicit a primary response in normal animals, and the distribution of radioactivity in the popliteal lymph nodes between 6 hours and 21 days later was studied by autoradiography. The recipient rabbits had either been primed by a single prior injection of unlabelled antigen, or made putatively tolerant by repeated neonatal administration of antigen, or were previously untreated. Localization of antigen in germinal centres, in a typical dendritic pattern, was marked in the primed animals throughout the period of observation; in those tolerant animals which had no detectable serum antibody initially and made no detectable antibody response such localization was not seen at any time; in the animals that had no previous contact with antigen there was no localization in germinal centres until about the time when antibody became detectable in the serum. Localization of radioactivity in medullary sinus macrophages did not differ significantly between the three groups. It is concluded that localization of these soluble antigens on the dendritic web in lymphoid follicles occurs as a consequence of the presence of circulating antibody. Uptake of the antigens by medullary macrophages, however, can occur in the absence of antibody. Although the degree of labelling of medullary macrophages was not evidently affected by the presence of antibody in these experiments, it is emphasized that the antibody levels, even in the primed animals, were low, and that this finding is unlikely to apply when the amount of antibody present is relatively much greater than the amount of antigen injected.