Langerhans cells are the major source of mRNA for IL-1β and MIP-1α among unstimulated mouse epidermal cells

Immunocompetent cells of the epidermis can interact by the elaboration and recognition of cytokines. Although much new information has been reported concerning the cytokines secreted by keratinocytes, little is known about cytokines derived from Langerhans cells (LC). To address this deficiency, we examined cytokine mRNA profiles in different epidermal preparations from BALB/c mice, taking advantage of the sensitive technique of polymerase chain reaction (PCR), after reverse transcription of mRNA. In assays of epidermal sheets separated from dermis by ammonium thiocyanate, mRNA for IL-1α, IL-1β, IL-6, IL-7, tumor necrosis factor α (TNFα), TNFβ1, granulocyte macrophage/colony-stimulating factor (GM-CSF), and macrophage inflammatory protein-lα (MIP-1α) were unequivocally present. By contrast, faint bands were detected for IL-4, IL-5, and interferon γ (IFNγ), and no PCR signal was detected for IL-2. Importantly, assays of epidermal cells (EC) dissociated with trypsin revealed similar mRNA profiles. To determine the effects of cell isolation, fluorescence-activated cell sorter (FACS)-purified Ia-EC were first analyzed; all of the previously cited cytokine mRNA were present except for IL-1β and MIP-1α. EC depleted of LC by a second technique, lysis using anti-Ia monoclonal antibody and complement, revealed similar profiles, with substantially reduced PCR signals for IL-1β and MIP-1α. Finally, FACS-purified LC (Iα+ EC) clearly expressed IL-lβ and MIP-lα mRNA, a finding that was verified by Southern blotting using internal oligo probes. We conclude that these cell-isolation procedures did not produce substantial alterations in basal mRNA profiles and that LC are the principal source of mRNA for IL-1β and MIP-1α among unstimulated EC in mice.