TNF and skin sensitization: While NiSO4 is able to directly initiate immune cell activation, it is well known that keratinocytes possess the ability to secrete tumor necrosis factor‐α (TNF‐α), interleukin‐1α (IL‐1α), and IL‐18 following skin sensitization.[64, 65, 66] These cytokines generate cutaneous inflammation, which culminates in the regulation of LC migration and in the subsequent accumulation of DCs in the draining lymph nodes.