Sensitization of the respiratory tract is an important occupational health challenge, and understanding the mechanistic basis of this effect is necessary to support the development of toxicological tools to detect chemicals that may cause it. Here we use the adverse outcome pathway (AOP) framework to organize information that may better inform our understanding of sensitization of the respiratory tract, building on a previously published skin sensitization AOP, relying on literature evidence linked to low-molecular-weight organic chemicals and excluding other known respiratory sensitizers acting via different molecular initiating events. The established key events (KEs) are as follows: (1) covalent binding of chemicals to proteins, (2) activation of cellular danger signals (inflammatory cytokines and chemokines and cytoprotective gene pathways), (3) dendritic cell activation and migration, (4) activation, proliferation, and polarization of T cells, and (5) sensitization of the respiratory tract. These events mirror the skin sensitization AOP but with specific differences. For example, there is some evidence that respiratory sensitizers bind preferentially to lysine moieties, whereas skin sensitizers bind to both cysteine and lysine. Furthermore, exposure to respiratory sensitizers seems to result in cell behavior for KEs 2 and 3, as well as the effector T cell response, in general skewing toward cytokine secretions predominantly associated with T helper 2 (Th2) response. Knowledge gaps include the lack of understanding of which KE(s) drive the Th2 polarization. The construction of this AOP may provide insight into predictive tests that would in combination support the discrimination of respiratory-sensitizing from non-and skin-sensitizing chemicals, a clear regulatory need.

The antigenic diversity within a panel of 63 Haemophilus ducreyi isolates was examined by Western blot (immunoblot) analysis with a pool of 238 well-characterized human antisera. When a serum pool adsorbed on a mixture of Haemophilus influenzae, H. parainfluenzae, and H. parahaemolyticus was used, the immunoprotiles suggested that prominent antigenic proteins involved in the human immune response have apparent molecular masses of 63, 42, 34 to 30, and 28.5 to 28 kDa. Preliminary subcellular localization revealed that these antigens are associated with the cellular membrane. Two subsets of antigens were discriminated by detergent extraction. There was no evidence that the antigen composition is altered by changing the growth conditions. With a serum pool adsorbed on the Haemophilus spp. mixture supplemented with Actinobacillus actinomycetemcomitans, Pasteurella ureae, Neisseria gonorrhoeae, and Escherichia coli, antigenic determinants more specific for H. ducreyi were identified. An immunodominant 28.5to 28-kDa protein was expressed by all H. ducreyi isolates. In the range from 34 to 30 kDa, 56 isolates revealed a dominant protein with variable molecular mass. By using both proteins (28.5 to 28 kDa and 34 to 30 kDa) as immunotypic markers, seven different immunopatterns were identified. Antigenic diversity among isolates from different geographical origins as well as from a single area was observed.Haemophilus ducreyi is a poorly known and fastidious microorganism causing chancroid, a sexually transmitted disease (STD) that is characterized by genital ulcers and by abcedation of the inguinal lymph nodes (6). Recently, chancroid has received more interest because it is emerging as the major cause of genital ulcer disease in several parts of the developing world, and it is reappearing in poor minority populations in Europe and the United States (10,14,16). In addition, several reports suggest that genital ulcer disease, in particular chancroid, is a risk factor for the sexual transmission of the human immunodeficiency virus (9). Little is known about the antigenic composition of H. ducreyi, and the nature of the immune response upon infection has been poorly studied. Serum immunoglobulin G (IgG) and IgM antibodies have been detected in patients with a clinical diagnosis of chancroid both by dot immunobinding and by an enzyme immunoassay (8,13). Western blot analysis of sera from normal and immunized rabbits has shown that rabbits immunized with H. ducreyi respond with a humoral immune response in which multiple antigenic polypeptides are detected. The most prominent antigens are reported to have apparent molecular masses of 79, 62, 55, 49, and 26 kDa (7) and of 67, 42, 22.5, and 20 kDa (12). However, the specificity of the antigens towards H. ducreyi has not been demonstrated.In the present study, the antigenic diversity occurring within a panel of H. ducreyi isolates was examined by Western blot (immunoblot) analysis. Prominent proteins involved in the human immune response and H. ducreyispecific antigens were iden...

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Abstract:Over the last decade, incredible progress has been made in the development of non-animal tests to assess contact hypersensitivity. Four methods have been successfully validated and Organisation for Economic Co-operation and Development (OECD) guidelines are available or soon will be. Currently validated methods are useful for hazard identification, classification and labeling. However, to achieve a complete replacement of animals in skin sensitization assessment, dose-response information and evaluation of relative skin sensitizing potency to support effective risk assessment are necessary. In this context, potency is based on the concentration of chemicals needed to induce a positive response. This will require a better understanding of the mechanisms determining potency, including pathway analysis and marker signature identification (selection of an appropriate immune-mediated response to serve as the basis), together with quantitative and qualitative correlations between marker signatures and potency of chemicals in relation with T cell responses. This review aims to discuss the state-of-the-art in the field of in vitro assessment of the no induction sensitization level of contact sensitizers.

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