Immune responses to infectious agents, especially viruses, are often associated with
extensive proliferation of T cells and transient enlargement of the lymphoid tissues. Since
the precursor frequency of T cells for specific antigen is low, the bulk of the T cells
proliferating in the primary response are presumably stimulated via non-antigen-specific
mechanisms, eg via cytokines elicited by the infectious agent concerned. Suchbystander'
stimulation of T cells occurs in mice injected with agents that elicit production of type I …