Increased C5a anaphylatoxin in the sera of psoriatic patients and patients with inflammatory dermatoses

Complement C3 deficient mice show more severe imiquimod-induced psoriasiform dermatitis than wild-type mice regardless of the commensal microbiota

The complement active product, C3a, and the receptor C3aR comprise an axis that exerts various biological functions, such as protection against infection. C3a is highly expressed in the inflamed skin and blood from patients with psoriasiform dermatitis. However, the role of the C3a/C3aR axis in psoriasiform dermatitis remains unclear because conflicting results using C3-/- mice have been published. In this study, to elucidate the contribution of commensal microbiota in C3-/- and wild-type (WT) mice were subjected to imiquimod-induced psoriasiform dermatitis under different housing conditions. C3-/- mice showed increased epidermal thickness and keratinocyte proliferation markers in the inflamed ear compared to WT mice upon treatment with IMQ. These inflamed phenotypes were observed in both cohoused and separately housed conditions, and antibiotic treatment did not abolish the aggravation of IMQ-induced psoriasiform dermatitis in C3-/- mice. These results suggested that the difference of commensal microbiota is not important for the C3-involved psoriasiform dermatitis. Keratinocyte hyperproliferation is a major feature of the inflamed skin in patients with psoriasiform dermatitis. In vitro experiments showed that C3a and C3aR agonists inhibited keratinocyte proliferation, which was abolished by introduction of a C3aR antagonist. Collectively, these results suggest that the C3a/C3aR axis plays a critical role in psoriasiform dermatitis development by inhibiting keratinocyte proliferation, regardless of the regulation of the commensal microbiota.

C5a/C5aR1 Pathway Is Critical for the Pathogenesis of Psoriasis

Psoriasis is one of the most common chronic inflammatory skin diseases, affecting ~2% of the population. The lack of characterization of the pathogenesis of psoriasis has hindered efficient clinical treatment of the disease. In our study, we observed that expression of complement component 5a receptor 1(C5aR1) was significantly increased in skin lesions of both imiquimod (IMQ) and IL23-induced psoriatic mice and patients with psoriasis. C5aR1 deficiency or treatment with C5a receptor 1 antagonist (C5aR1a) in mice significantly attenuated psoriasis-like skin lesions and expression of inflammatory cytokines and chemokines. Moreover, C5aR1 deficiency significantly decreased IMQ-induced infiltration of plasmacytoid dendritic cells (pDCs), monocytes and neutrophils in psoriatic skin lesions and functions of pDCs, evidenced by the remarkable reduction in the IMQ-induced production of interferon-α (IFN-α) and tumor necrosis factor α (TNF-α), and FMS-like tyrosine kinase 3 ligand (FLT3L)-dependent pDCs differentiation. Accordingly, in vitro treatment with recombinant C5a accelerated pDCs migration and the differentiation of bone marrow cells into pDCs. Furthermore, biopsies of psoriatic patients showed a dramatic increase of C5aR1⁺ pDCs infiltration in psoriatic skin lesions, compared to healthy subjects. Our results provide direct evidence that C5a/C5aR1 signaling plays a critical role in the pathogenesis of psoriasis. Inhibition of C5a/C5aR1 pathway is expected to be beneficial in the treatment of patients with psoriasis.

Natural killer cell activity, serum immunoglobulins, complement proteins, and zinc levels in patients with psoriasis vulgaris

The role of the immune system in patients with psoriasis vulgaris (PV) was investigated. The genetic and immunological basis for psoriasis is still unknown. Because of the reports of immunological defects in this disease, we investigated serum levels of immunoglobulins IgG, IgM, IgA, complement proteins C3, C4, serum zinc (Zn) levels and natural killer (NK) cell activities. Skin lesions of the psoriatic patients involved in the study comprised less than 10 % of the total body and the disease was in a stationary period. Zn levels were measured by atomic absorption spectrophotometry. NK cell activity was measured by 51Cr (Na2 51CrO4). IgG, IgA, IgM, C3 and C4 assays were done by liquid-phase immunoprecipitation assay with nephelometric endpoint detection. IgG, IgA, C3 and C4 levels were significanty higher in patients with PV than in healty controls (p < 0.05). However, NK cell activity, serum Zn and IgM levels did not show significant differences between these two groups. There are changed immunological responses, which may play an important role in the pathogenesis of the disease. Many controversial results have been related to immunological parameters in psoriatic patients. Therefore, more detailed studies in this field need to be done to determine the relationship between psoriasis and the immune system.

Psoriasis and leukocyte chemotaxis

Transepidermal migration of leukocytes, with resultant formation of microscopic or macroscopic sterile subcorneal pustules is a phenomenon characteristically noted in psoriasis and related sterile pustular dermatoses. It is natural to assume the presence of potent neutrophil chemotactic substances in the subcorneal portion of the lesional epidermis, because this location is the target of the in vivo leukocyte chemotaxis. In fact, crude psoriasis scale extracts show remarkably high neutrophil chemotactic and activating properties as compared with those of other non-psoriatic inflammatory dermatoses. We isolated a psoriatic leukotactic factor (PLF) having a molecular mass of around 12 kD, distinct from those common to other inflammatory changes involving the skin or those released by bacteria. Further analysis of PLF identified C5 cleavage fragments, together with other chemotactic peptides, such as those derived from monocytes. Likewise, potent low-molecular-mass chemotactic factors, including cell membrane lipid derived chemotactic factor, e.g. leukotriene B4, are also increased in psoriatic lesions, as in other nonpsoriatic inflammatory dermatoses. However, their activity to stimulate the generation of oxygen radicals in neutrophils was found to be much weaker than that of PLF. The peripheral blood leukocytes from active psoriatic patients show enhanced function in chemotaxis, phagocytosis, active oxygen production, and enzyme release; patients' sera contain substances such as anaphylatoxins that activate leukocyte function. Further research is required for clearer understanding of the series of events resulting in the leukocyte chemotaxis, as well as for the elucidation of the background immunoregulatory mechanisms.