T helper type 1 cytokines and keratinocyte growth factor play a critical role in pseudoepitheliomatous hyperplasia initiation during cutaneous leishmaniasis.

Pseudoepitheliomatous hyperplasia (PEH) is an exuberant proliferation of the epidermis. The underlying mechanism(s) that lead to PEH have not been completely elucidated. Here, we characterize PEH during the healing stages of cutaneous leishmanial ulcers in mice. During experimental cutaneous leishmaniasis (CL) C57BL/6 mice produce PEH, and BALB/c do not. A series of immunohistochemical and immunological studies were performed to identify the secretory products of PEH regulation. We observed that the distribution of TNF-alpha and IFN-gamma under PEH had a stripe-like diffuse pattern and localized in the upper part of the papillary dermis directly under the proliferating epidermis. Macrophages were identified as the major source of TNF-alpha (56.3%). The importance of IFN-gamma and TNF-alpha in PEH development was proven by the initiation of PEH after three intralesional injections of TNF-alpha and IFN-gamma every three days in infected BALB/c mice. In C57BL/6 mice, keratinocyte growth factor (KGF) expressing cells were found immediately under the basal membrane of the hyperplastic epidermis in comparison with sporadic KGF positive cells deep in the dermis of BALB/c mice. Quantitative RT-PCR analysis demonstrated increased KGF and KGF receptor expression in uninfected C57BL/6 mice as compared to BALB/c mice. These data indicate that Th1 cytokines and KGF play a critical role in PEH initiation during CL.