Human plasmacytoid dendritic cells express receptors for anaphylatoxins C3a and C5a and are chemoattracted to C3a and C5a.

The presence of plasmacytoid dendritic cells (pDC) was recently demonstrated in lesions of inflammatory skin diseases. Since anaphylatoxins or their precursors were also found in such lesions, we investigated a possible interaction between pDC and anaphylatoxins C3a and C5a. pDC precursors isolated from peripheral blood did not express the receptors for C3a and C5a, complement C3a receptor (C3aR) and complement C3a receptor (C5aR). If these pDC precursors were cultured with IL-3, the resultant immature pDC expressed both receptors. Expression of C3aR and C5aR could also be demonstrated on pDC in lesions of cutaneous lupus erythematosus and allergic contact dermatitis. Such pDC were immature since they lacked the expression of the maturation marker CD83. Blood-derived pDC matured with CpG oligonucleotides downregulated the receptors. Immature pDC responded to C3a and C5a (but not C3adesArg) stimulation with increased F-actin polymerization and chemotactic migration. In contrast, interferon alpha production, surface molecule expression, and T-cell stimulatory capacity were not significantly modulated by C3a or C5a. Thus, immature pDC represent another type of antigen-presenting cell that express C3aR and C5aR, and respond to anaphylatoxins with chemotaxis. This might be relevant in the direction of pDC to cutaneous lesions of inflammation, for example, in lupus erythematosus or contact dermatitis.