Antigen handling in relation to ageing

The distribution of a soluble antigen, 3H-BSA was studied in tissues (blood, liver, spleen, kidneys, lymph nodes, thymus and lungs) after intravenous injection into cohorts of the Fischer-344 rat colony of the National Institute on Aging that is maintained at Charles River Breeding Laboratories. The ten groups for which results are reported were maintained during the experimental procedures as the cohorts received from the "colony". Both the primary and secondary antigen injection were administered as 1 mg of protein per 50 g body weight. All the highly vascularized tissues of those studied showed the same relative distribution of antigen with age as the blood; i.e. a lower percentage of the injection at both extremes of the age span studied, 2 and 24 months of age. These age-related differences are more pronounced with primary than secondary immunization. Because of the higher level of antigen in the liver than blood, it is concluded that a specific localization of antigen occurs in the liver. Products of in vivo metabolism of 3H-BSA are isolated as liver nucleopeptides and are also co-isolated with liver polysomes. These particular forms of metabolized antigen have been shown to be immunogenic in other studies. The co-isolated polysome antigen in the present findings is reduced quantitatively in the older rats (for example, in 24 months compared to 12 month). The study of the changes in antigen parceling at the cellular and subcellular level, which occurs with ageing, is likely to provide insight into antigen induction.