Abnormalities in the alternative pathway of complement in psoriasis

Complement Activation in Inflammatory Skin Diseases

The complement system is a fundamental part of the innate immune system, playing a crucial role in host defense against various pathogens, such as bacteria, viruses, and fungi. Activation of complement results in production of several molecules mediating chemotaxis, opsonization, and mast cell degranulation, which can contribute to the elimination of pathogenic organisms and inflammation. Furthermore, the complement system also has regulating properties in inflammatory and immune responses. Complement activity in diseases is rather complex and may involve both aberrant expression of complement and genetic deficiencies of complement components or regulators. The skin represents an active immune organ with complex interactions between cellular components and various mediators. Complement involvement has been associated with several skin diseases, such as psoriasis, lupus erythematosus, cutaneous vasculitis, urticaria, and bullous dermatoses. Several triggers including auto-antibodies and micro-organisms can activate complement, while on the other hand complement deficiencies can contribute to impaired immune complex clearance, leading to disease. This review provides an overview of the role of complement in inflammatory skin diseases and discusses complement factors as potential new targets for therapeutic intervention.

Inflammatory and immune reactions associated with stratum corneum and neutrophils in sterile pustular dermatoses

In this review we present our own experimental findings as well as those from the literature related to the pathomechanisms for the inflammatory changes in psoriasis and its related diseases. A growing body of evidence has indicated that T cell-mediated immunity plays an important role in triggering and maintenance of psoriatic lesions. It has been revealed that lymphokines produced by activated T cells in psoriatic lesions have a strong influence on the proliferation of the epidermis. Characteristic neutrophil accumulation under the stratum corneum can be observed in the highly inflamed areas of psoriatic lesions. These neutrophils are chemotactically attracted and activated there by synergistic action of chemokines, IL-8 and Gro-alpha released by stimulated keratinocytes, and particularly by C5a/C5a des arg produced via the alternative complement pathway activation. We demonstrated that the infiltrating neutrophils adhere to iC3b-opsonized corneocytes to produce active oxygen and probably lysosomal enzymes. From a close relationship observed between neutrophil accumulation and high mitotic ratio of the lesional epidermis, we think that these stimulated neutrophils influence the growth and differentiation of epidermal keratinocytes. Aberrant expression of HLA-DR on neutrophils suggests their activation of infiltrating T cells in the presence of bacterial superantigen. These T cells in turn influence the transepidermal neutrophil migration through the effect of their cytokines on the keratinocyte production of proinflammatory mediators including IL-8 and C3. In this review we discuss the pivotal roles played by stratum corneum and neutrophils in several skin diseases, where neutrophils accumulate beneath the stratum corneum in a sterile condition.

Systemic complement activation in psoriasis vulgaris

Nineteen patients with psoriasis vulgaris and no other cause for systemic complement activation were studied for evidence of such activation. There was a marked elevation in serum C5b-9 complexes with no other significant complement abnormalities, and no correlation between C5b-9 levels and disease activity. This is the most detailed study of complement in psoriasis yet attempted and confirms that complement activation is a feature of psoriasis vulgaris.

Psoriasis is a visible manifestation of the skin's defense against micro-organisms

The recent discovery that human epidermal cells themselves make and secrete the components necessary for activation of the alternative complement pathway appears to provide an explanation for how human skin is ordinarily able to avoid colonization by molds and other organisms. It also helps clarify the mechanisms underlying clinical and laboratory findings seen in chronic mucocutaneous candidiasis, dandruff, and psoriasis. Psoriasis seems best explainable as a visible, late stage of the inflammatory sequelae of activation of the alternative complement pathway in the epidermis.

The role of complement-derived mediators in inflammatory skin diseases

The complement system represents an important nonspecific skin defense mechanism. Its activation leads to the generation of products that not only help to maintain normal host defenses but also mediate inflammation and tissue injury. Proinflammatory products of complement include large fragments of C3 with opsonic and cell-stimulatory activities (C3b and C3bi), low molecular weight anaphylatoxins (C3a, C4a, and C5a), and membrane attack complex. Among them C5a or its degradation product C5a des Arg seems to be the most important mediator because it exerts a potent chemotactic effect on inflammatory cells. Intradermal administration of C5a anaphylatoxin induces skin changes quite similar to those observed in cutaneous hypersensitivity vasculitis that occurs through immune complex-mediated complement activation. Complement activation is involved in the pathogenesis of the inflammatory changes in autoimmune bullous dermatoses. In pemphigus complement activation by pemphigus antibody in the epidermis seems to be responsible for the development of characteristic inflammatory changes termed eosinophilic spongiosis. In bullous pemphigoid (BP) interaction of basement membrane zone antigen and BP antibody leads to complement activation that seems to be related to leukocytes lining the dermoepidermal junction. Resultant anaphylatoxins not only activate the infiltrating leukocytes but also induce mast cell degranulation which facilitates dermoepidermal separation and eosinophil infiltration. Similar complement activation seems to play a more direct role in the dermoepidermal separation noted in epidermolysis bullosa acquisita and herpes gestationis. Anaphylatoxin generation via the alternative pathway activation under light irradiation is implicated in the development of the immediate erythematous phototoxic reactions induced by such well-known chemicals as porphyrin, chlorothiazide, demethylchlortetracycline, and chlorpromazine.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy of bimolane in the Malassezia ovalis model of psoriasis

Bimolane, an analog of razoxane has been used in China with comparable efficacy but less toxicity than razoxane in the treatment of psoriasis. In an attempt to characterize further its mode of action it was administered both systemically and topically in the Malassezia ovalis animal model of psoriasis. Intravenous methotrexate and topical 0.1% betamethasone valerate were also used as positive control treatments. The animal model of psoriasis was effectively treated by bimolane, both systemically and topically, and also by parenteral methotrexate and topical betamethasone valerate. The time course of bimolane's effect with this model was different from methotrexate's suggesting the possibility of a different mode of action. Because bimolane, like razoxane, is an ethylene diamino tetraacetate acid (EDTA) derivative, it is possible that its effects on this reaction relate to its chelating properties and that inhibition of complement activation is important to its mode of action.

Complement activation in psoriasis

Plasma from 16 patients with psoriasis and 12 healthy control subjects were measured for iC3b, C4d, and Bb fragments generated by complement activation. Plasma concentrations for iC3b, C4d, and Bb fragments were found to be significantly increased in the patients with psoriasis. The highest concentrations of these complement activation fragments were seen in patients with erythrodermic pustular psoriasis, psoriatic arthritis, and Reiter's syndrome. The serum concentrations of complement components and regulatory proteins were normal or elevated in almost all samples.

Acute psoriasis associated with Lancefield Group C and Group G cutaneous streptococcal infections

Involvement of Streptococcus pyogenes (beta haemolytic streptococcus, Lancefield Group A) infection, usually of the throat, in acute exacerbations of psoriasis is well known. We report here two cases of an acute psoriatic eruption associated in one patient with Group C streptococcal cellulitis and in another with Group G streptococcal intertrigo.

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.

Demonstration of anaphylatoxins C3a, C4a and C5a in the scales of psoriasis and inflammatory pustular dermatoses

Complement components C3a, C4a and C5a were assayed in corneal scale extracts from psoriasis and other dermatoses characterized by sterile subcorneal pustules, using radioimmunoassay. Larger amounts were detected in psoriasis and related pustular dermatoses than in extracts of non-inflammatory stratum corneum. It is concluded that complement is activated via the classical pathway and releases the neutrophil chemotactic fragment C5a.

Increased anaphylatoxins (C3a and C4a) in psoriatic sera

We measured C3a and C4a anaphylatoxins in the serum of 56 psoriatic patients and 36 healthy control subjects by radioimmunoassay in order to clarify the mechanism of complement activation occurring in psoriatic lesions. Whereas a small amount of anaphylatoxins were demonstrable even in the sera of healthy adults, the serum concentrations of C3a and C4a anaphylatoxins were significantly higher in psoriatic patients than those in non-psoriatic controls. The increased serum anaphylatoxin levels did not correlate well with either the extent or the activity of the skin lesions, but a comparison of anaphylatoxin levels in 10 patients before and after successful treatment of skin lesions showed that the serum anaphylatoxin levels decreased with improvement of the skin lesions. Our results suggest that complement activation takes place in psoriatic patients chiefly via the classical pathway.

Involvement of complement in psoriasis and atopic dermatitis--measurement of C3a and C5a, C3, C4 and C1 inactivator

Normal complement components and activation products were determined in the peripheral blood of 35 patients with atopic dermatitis (AD) and 24 patients with psoriasis at a mild to intermediate stage. None of the patients had received systemic or local steroid therapy 6 weeks prior to blood collection. Levels of C3, C4 and C1 inactivator (C1 INA) were determined in serum by radial immunodiffusion, whereas C3a and C5a levels were measured by radioimmunoassay. In comparison to healthy non-atopic controls, the levels of C3, C4 and C1 INA were found to be significantly increased in both diseases. No substantial differences were detected between patients with psoriasis vulgaris and psoriasis guttata, which suggests that the dissimilarities found were not due to preceding or concomitant infections. In AD, there was a tendency towards increased C3a levels, whereas in psoriasis, C3a levels were significantly increased. In both diseases, no measurable amounts of C5a could be detected. The results indicate that, in both AD and psoriasis, the complement participates in the inflammatory process. Elevated levels of C3a suggest that there is a continuous activation of the complement system leading to the generation of inflammatory mediators.