Britz , Askenase , Ptak , Steinman

Topical application of picryl chloride (PCL), 1 the chemically reactive form of the tr initrophenyl (TNP) hapten, regularly induces a contact hypersensitivity reaction (CS) that is of the long-lived type (>3 wk) (1). However, when T N P is coupled to cells in vitro and these cells are used for immunizat ion, three different immunological outcomes m a y ensue depending on the route of administration and the type o f cell to which T N P is coupled. One outcome is the development of specific immunological unresponsiveness (tolerance). This results when TNP-coupled lymphocytes or macrophages (peritoneal-exudate cells, PEC) are injected intravenously and is probably a result of the induction of specific suppressor T cells (1-3). A second outcome is the development of an evanescent form of CS that results when T N P P E C are administered under conditions that avoid rapid activation of the suppressor circuit. This can be done by pretreating recipient mice with a low dose of cyclophosphamide or injecting the TNP-labeled cells subcutaneously so that the initial contact of antigen with the immune system takes place in the draining lymph nodes rather than in the spleen (1-3). A third outcome is the development of a long-lived form of CS, similar to that achieved by topical application of PCL. This form of immuni ty also occurs when TNP-coupled epidermal Langerhans cells are used for immunizat ion, even when these cells are injected intravenously and no cyclophosphamide is used (1). In fact, T N P coupled Langerhans cells induce CS when coadministered with an immunosuppressive inoculum of TNP-PEC. This implies that antigen presentation on Langerhans cells,