Nature of 'memory' in T cell mediated antibacterial immunity: cellular parameters that distinguish between the active immune response and a state of 'memory'

Abstract

Immunizing infection in mice with Listeria monocytogenes resulted in the generation of two distinct states of immunologic reactivity. There were generated a short lived state of active immunity that functioned to urgently eliminate the infecting organism from the tissues, and a long lived state of increased immunologic potential that enabled the host to respond to secondary infection in an accelerated manner. Short lived active immunity was mediated by replicating T cells and expressed by activated macrophages, and it ended when these cell types disappeared from the tissue soon after complete elimination of the parasite. Long lived immunologic potential was associated with a persistent level of delayed sensitivity and with the presence of a small number of nonreplicating protective T cells. It is suggested that the state of delayed sensitivity represents a state of immunologic T cell memory of the cell mediated type.