Background Epidermal Langerhans cells (LCs) play an important role in cutaneous immunological reactions. Freshly obtained or intraepidermal LCs are incapable of activating autologous naive T cells. However, when they are cultured for 2–3 days, LCs are able to activate autologous T cells. It has been proposed that haptoglobin (Hp) is the inhibitor that prevents LC functional transformation in the skin. Abundant Hp has been found in the cytoplasm of epidermal LCs. However, the source of Hp in LCs has not been addressed.

Objectives To determine the expression of Hp in epidermal cells, and to provide evidence that there is a functional relationship between LCs and keratinocytes (KCs) through Hp.

Methods Normal human epidermal cells and HaCaT cells were used for detection of Hp mRNA by in situ hybridization and reverse transcription–polymerase chain reaction, and Hp protein by immunohistochemical staining, immunofluorescence counterstaining and Western blotting.

Results Hp mRNA was expressed in normal human KCs and HaCaT cells, but not in normal human epidermal LCs. Hp protein was detected by immunohistochemical staining and immunofluorescence counterstaining in CD1a+ epidermal dendritic cells (LCs), but not in KCs. Hp protein was weakly expressed by HaCaT cells.

Conclusions Hp mRNA is present in normal human KCs and HaCaT cells, suggesting that they have the potential to synthesize Hp protein. Normal human epidermal LCs are unable to synthesize Hp protein by themselves, although they have abundant Hp protein in their cytoplasm. It is likely that LCs acquire Hp through an exogenous pathway.