Maturation of epidermal Langerhans cells: increased expression of beta- and gamma-actin isoforms as a basis of specialized cell functions

Epidermal Langerhans cells (LC) represent immature dendritic cells. During in vitro culture in the presence of keratinocytes they mature into patent i mmunostimulatory cells for naive T cells. This process is thought to simula te in vivo maturation of LC following activation by antigen contact. Matura tion of LC is accompanied by morphological alterations. Applying a differen tial screening procedure we isolated differentially expressed cDNAs involve d in the maturation events including cDNAs of the cytoskeletal actin isofor ms beta- and gamma-actin, Stronger signals with hybridization probes derive d from cultured LC compared with probes derived from freshly isolated LC in dicate upregulation of actin expression. Upregulated expression of actin wa s confirmed by RT-PCR, Western blot and immunofluorescence analysis. Staini ng with fluorescence-labelled phalloidin that selectively binds to polymeri zed F-actin, indicates an increase in F-actin levels in cultured LC. Thus o ur data show that maturation of LC, which involves formation of dendritic s tructures and movement of formerly immobile cells, is accompanied by augmen ted expression of actin and formation of additional actin filaments. Furthe rmore, actin mRNA, often used as reference to assess mRNA amounts for North ern blotting or competitive RT-PCR because of its high and ubiquitous expre ssion, an inappropriate standard for the analysis of LC and DC.