Assimilation, tolerance and the end of innocence

RESUMO

Immunological activity is conceptually and biochemically related to digestion and assimilation processes. Food materials comprise the vast majority of foreign macromolecules handled by the organism. Lympphocyte activation involves partial digestion ("processing") of both foreign and self molecules. Immunoglobulins accelerate the clearance (by opsonization) and intracellular digestion of materials to which they bind. Immunological activity may, therefore, be seen as a network of processes facilitating the assimilation of foreign materials. This same network is continuously incorporating new (emergent) cellular and molecular components into the lymphoid system. In oral tolerance, the organism is usually seen as becoming permissive to the presence of previously ingested antigens, as if their presence remained unacknowledged. However, the exposure of orally-tolerant animals to the tolerated antigens blocks the concomitant induction of unrelated immune responses. The assimilation of tolerated antigens to the network of lymphocyte activities, therefore, may have broad consequences. We claim that these "indirect effects"of the tolerated antigen cannot be ascribed to "innocent bystander"suppression, i.e. to fortuitous proximity to cells releasing suppressive cytokines.