Human papillomavirus type 16 (HPV16) is an oncogenic virus that causes persistent infections in cervical epithelium. The chronic nature of HPV16 infections suggests that this virus actively evades the host immune response. Intraepithelial Langerhans cells (LC) are antigen-presenting cells that are critical in T-cell priming in response to viral infections of the skin. Here we show that HPV16 infection is directly associated with a reduction in the numbers of LC in infected epidermis. Adhesion between keratinocytes (KC) and LC, mediated by E-cadherin, is important in the retention of LC in the skin. Cell surface E-cadherin is reduced on HPV16-infected basal KC, and this is directly associated with the reduction in numbers of LC in infected epidermis. Expression of a single viral early protein, HPV16 E6, in KC reduces levels of cell surface E-cadherin thereby interfering with E-cadherin-mediated adhesion. Through this pathway, E6 expression in HPV16-infected KC may limit presentation of viral antigens by LC to the immune system, thus preventing the initiation of a cell-mediated immune response and promoting survival of the virus.Human papillomaviruses (HPV) cause persistent disease, despite producing immunogenic proteins throughout the replicative cycle. These viruses are therefore likely to possess an army of mechanisms to avoid the host immune system. Some types of HPV, in particular type 16, are strongly associated with the development of cancer after infections of the cervical epithelium (54). Consequently, the chronic nature of the infection, in association with high-risk oncogenic types of HPV, results in an increased risk of cellular transformation and malignancy.HPV is a nonlytic virus that is only permissive for viral replication in epidermal keratinocytes (KC). The ability of the virus to influence the immune system is therefore limited to the localized environment of the infected epidermis. Furthermore, activation of the adaptive immune response to HPV is dependent on cross-presentation of viral antigens to antigen-presenting cells (APC) resident in the skin (43). In the present study we explore the influence of HPV on the host's capacity to initiate the immune response by reducing numbers of APC resident at the site of infection.Langerhans cells (LC) are the epidermal contingent of the potent antigen-presenting dendritic cells (34) and constitute the primary APC in the skin. Immature LC form a contiguous network throughout the epithelium. Under steady-state conditions, CD14ϩ , E-cadherin-negative LC precursors migrate from the dermis into the epidermis in response to macrophage inflammatory protein 3␣ (MIP-3␣) (9) and differentiate into CD14ϩ , E-cadherin-positive immature LC when exposed to transforming growth factor ␤1 (TGF-␤1) (25). Both MIP-3␣ and TGF-␤1 are constitutively expressed by KC. Immature LC initiate migration from the epidermis in response to proinflammatory stimuli such as tumor necrosis factor alpha and interleukin-1␤ (12, 49). These cells become responsive to MIP-3␤, which directs the...

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