The human epidermis serves 2 crucial barrier functions: it protects against water loss and prevents penetration of infectious agents and allergens. The physiology of the epidermis is maintained by a balance of protease and antiprotease activities, as illustrated by the rare genetic skin disease Netherton syndrome (NS), in which impaired inhibition of serine proteases causes severe skin erythema and scaling. Here, utilizing mass spectrometry, we have identified elastase 2 (ELA2), which we believe to be a new epidermal protease that is specifically expressed in the most differentiated layer of living human and mouse epidermis. ELA2 localized to keratohyalin granules, where it was found to directly participate in (pro-)filaggrin processing. Consistent with the observation that ELA2 was hyperactive in skin from NS patients, transgenic mice overexpressing ELA2 in the granular layer of the epidermis displayed abnormal (pro-)filaggrin processing and impaired lipid lamellae structure, which are both observed in NS patients. These anomalies led to dehydration, implicating ELA2 in the skin barrier defect seen in NS patients. Thus, our work identifies ELA2 as a major new epidermal protease involved in essential pathways for skin barrier function. These results highlight the importance of the control of epidermal protease activity in skin homeostasis and designate ELA2 as a major protease driving the pathogenesis of NS.

Syngenic C57BL/6 mice (H-2b) vaccinated with mitomycin C-treated L12R4 T lymphoma cells develop protective immunity toward the MHC class II-negative tumor cells. In the present study, we characterize the nature, mode of function, and specificity of the effector cells in this immunity. These cells are TCR-specific CD8+ T lymphocytes with effector function in vitro as well as in vivo upon transfer to naive mice. They produce high levels of IFN-γ and TNF-α, but little or no IL-4. By means of TCRβ-negative variant L12R4 cells, P3.3, and TCR-Vβ2 cDNA-transfected and TCR-Vβ2-expressing P3.3 lymphoma cells, we found that a significant part of the effector T cells are specific for the Vβ12 region. The growth inhibition of L12R4 cells in vitro was inhibited by anti-H-2, anti-Kb, and anti-Db mAb. Furthermore, vaccination with Vβ12 peptide p67–78, which binds to both Kb and Db MHC class I molecules, induces partial protection against L12R4 T lymphoma cells. Thus, self-reactive TCR-Vβ-specific, Kb-, or Db-restricted CD8+ T cells mediate inhibition of T cell lymphoma growth in vitro and in vivo.