Effects of immunological responsiveness on Langerhans cell behavior in contact sensitization

The epicutaneous application of haptens results in a functional activation of the antigen-presenting Langerhans cells (LCs) which is necessary for the induction of contact sensitivity. In this ultrastructural study, we investigated the effects of the immune response on these cellular properties of the LCs by using 2 strains of guinea pigs with genetically determined high and non responsiveness, respectively, to the strong sensitizer 2,4-dinitrochlorobenzene (DNCB). After skin painting, both strains showed a similar cellular and endocytotic activation of the LCs and a similar intraepidermal localization of DNCB on immunoelectron microscopical visualization. There were however few LC-lymphoid cell interactions in the non responders, in contrast to numerous such appositions in the other strain. Intravenous tolerization with 2,4-dinitrobenzene-1-sulfonic acid, which is known to block the DNCB receptor of T cells, hampered the lymphoid cell interactions in the DNCB treated high responders, but it did not affect the LC activation. These in vivo observations demonstrate that the hapten-induced changes of the LC properties is the initial, T-cell independent event in contact sensitization.