Contact allergens are essentially soluble haptens (low in molecular weight) and, as such, have the physico-chemical properties that allow them to cross the stratum corneum of the skin. They can only cause their response as part of a complete antigen, involving their association with epidermal proteins forming hapten-protein conjugates. This, in turn, requires them to be protein-reactive. The conjugate formed is then recognized as a foreign body by the Langerhans cells (LCs) (and in some cases other Dendritic cells (DCs)), which then internalize the protein; transport it via the lymphatic system to the regional lymph nodes; and present the antigen to T-lymphocytes. This process is controlled by cytokines and chemokines – with tumor necrosis factor alpha (TNF-α) and certain members of the interleukin family (1, 13 and 18) – and their action serves either to promote or to inhibit the mobilization and migration of these LCs. As the LCs are transported to the lymph nodes, they become differentiated and transform into DCs, which are immunostimulatory in nature. Once within the lymph glands, the differentiated DCs present the allergenic epitope associated with the allergen to T lymphocytes. These T cells then divide and differentiate, clonally multiplying so that if the allergen is experienced again by the individual, these T cells will respond more quickly and more aggressively. White et al. have suggested that there appears to be a threshold to the mechanisms of allergic sensitisation by ACD-associated allergens (1986).
Kim, Sun Bean; Kim, Do Kyung; Byun, Sun Jeong; Park, Ji Hye; Choi, Jin Young; Park, Young Nyun; Kim, Do Young (2015-12-01). "Peliosis hepatis presenting with massive hepatomegaly in a patient with idiopathic thrombocytopenic purpura". Clinical and Molecular Hepatology. 21 (4): 387–392. doi:10.3350/cmh.2015.21.4.387. ISSN 2287-2728. PMC 4712167. PMID 26770928. External links
Merck Manual: Hepatomegaly