The Center for Alternatives to Animal Testing is an academic center affiliated with the Division of Toxicological Sciences in the Department of Environmental Health Sciences of the Johns Hopkins University Bloomberg School of Public Health.

 

Johns Hopkins School of Public Health

Commemorative Booklet for CAAT 20th Anniversary Symposium

Haptens Differ Immunologically from Irritants by Enabling T-Cells to Promote IL-12 Secretion from Antigen Presenting Cells

Sharmila Masli1 and J. Wayne Streilein2
1Schepens Eye Research Institute, Boston and 2Harvard Medical School, Boston

While it is known that haptens differ from irritants in that the former molecules have the unique ability to induce hapten-specific T cells that mediate contact hypersensitivity response, the molecular reasons for differential cutaneous responses to these two classes of chemicals are not clearly understood. In this study, haptens and irritants were compared for their capacity to lower the threshold of T-cell activation and to promote IL-12 production by antigen-presenting cells (APC).

Draining lymph node T cells isolated from mice (BALB/c) exposed epicutaneously to hapten (DNFB) vs. irritant (Croton oil) were stimulated in vitro with anti-CD3 antibodies and assayed for proliferation and IFN-y secretion. Hapten- or irritant-treated murine macrophage hybridoma cells (APCs) were assessed for IL-12 secretion when cultured in the presence of syngeneic T cells.

Our results revealed that five days after epicutaneous exposure, T cells isolated from hapten-treated mice proliferated vigorously and secreted high levels of IFN-y, compared to T cells from irritant-exposed mice. No such difference was observed with T cells removed 24 hrs after epicutaneous exposure. In addition, hapten-treated macrophage hybridoma cells cultured in the presence of naive syngeneic T cells secreted significantly higher levels of IL-12 than did irritant-treated hybridoma cells. These results suggest that haptens differ immunologically from irritants in their capacity to promote hapten-specific T cell interactions with APCs, which in turn cause the latter to secrete IL-12, the key factor responsible for generating contact hypersensitivity-mediating Th1 cells.

These findings may presage the development of in vitro assays designed to distinguish haptens from irritants and to predict which chemicals will function as haptens in individual subjects.