Cellular Basis for Immunologic Memory

Abstract

AFTER exposure to an antigen resulting in a primary immune response, experimental animals and human subjects possess the ability to react specifically and in accelerated fashion to a second exposure to the same antigen. This immunological memory presumably involves specific cells, but it is not known whether it involves generation of an increased number of cells or increased synthetic (or some other) ability in individual cells. Nobody has yet identified a cell which was generated by a previous contact with a specific antigen. Lymphocytes present in the circulation of rats have been shown to carry memory¹, and recent work has established that many such cells are thymus-derived and important in many aspects of the immune response^2,3. Because they are long lived and constantly re-circulating throughout the peripheral lymphoid organs, thymus-derived cells make ideal candidates for the carriage of memory. Indeed, memory can be diminished by killing cells in this sub-population⁴.