Initiator and recruited T lymphocytes are distinct subclasses of T lymphocytes

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Abstract
In previous studies we found that the generation of a cell‐mediated immune reaction required interaction between sensitized initiator T lymphocytes (ITL) and syngeneic recruited T lymphocytes (RTL). ITL were sensitized in vitro against allogeneic mouse fibroblasts and injected into a footpad of syngeneic recipient mice. ITL were observed to migrate from the connective tissues of the footpad to the draining popliteal lymph node (PLN). Sensitized ITL recruited RTL from the blood circulation into the PLN. This recruitment led to the generation of immunospecific effector and memory lymphocytes.In the present study we investigated the cellular characteristics of ITL and RTL. We found that both ITL and RTL were positive for Thy‐1 antigen, and were absent from B mice. However, ITL and RTL differed in their response to various treatments. ITL were sensitive to adult thymectomy and resistant to antithymocyte serum (ATS). RTL were resistant to adult thymectomy and sensitive to ATS. Sensitized ITL were adherent to nylon wool or histamine‐rabbit serum albumin‐Sepharose, while RTL were not retained on such columns.ITL and RTL also differed in their relative distributions in various lymphoid organs and migratory pathways. The thymus demonstrated ITL but not RTL activity. In contrast, lymph node lymphocytes were a rich source of RTL, but had no detectable ITL activity. Both ITL and RTL could be demonstrated in the spleen. Thus, ITL and RTL functions are mediated by distinct subclasses of T lymphocytes which reside in particular compartments of the immune system.