Human keratinocytes exposed to a clinical strain of Leishmania tropica can result in parasite internalization.

Cutaneous Leishmaniasis (CL) due to Leishmania tropica is a public health burden in Morocco. The increasing clinical polymorphism challenges its proper diagnosis and treatment. Although the immunopathogenesis of CL due to L. tropica has been documented, the role of keratinocytes, a critical cell type in skin immunity, has never been investigated in this pathology. Overall, keratinocytes play a crucial role in the recognition and early immune response to Leishmania parasites upon skin inoculation, influencing the local immune response by producing early cytokines that shape anti-leishmanial immune responses. Moreover, they respond differently to each Leishmania species, influencing disease outcomes and helping create a unique microenvironment tailored to each species, thus affecting disease progression. Herein, we have conducted in vitro infection of the human keratinocytes HaCaT cell line with Moroccan clinical strains of L. tropica and L. major. Through flow cytometry and imaging flow cytometry, we show that keratinocytes are infected with both Leishmania species and that they internalize L. tropica parasites. We also report that infection with L. tropica exhibits a higher infection frequency in keratinocytes compared to L. major. These findings support the potential involvement of keratinocytes in the early stages of cutaneous infection. However, further investigations are required to elucidate their role in modulating the local immune response. Our study is a first step in the investigation of keratinocytes involvement during CL due to L. tropica and opens new perspectives for research into CL-specific skin immune mechanisms.