Fc gamma receptors on keratinocytes in psoriasis

Melanin's Journey from Melanocytes to Keratinocytes: Uncovering the Molecular Mechanisms of Melanin Transfer and Processing

Skin pigmentation ensures efficient photoprotection and relies on the pigment melanin, which is produced by epidermal melanocytes and transferred to surrounding keratinocytes. While the molecular mechanisms of melanin synthesis and transport in melanocytes are now well characterized, much less is known about melanin transfer and processing within keratinocytes. Over the past few decades, distinct models have been proposed to explain how melanin transfer occurs at the cellular and molecular levels. However, this remains a debated topic, as up to four different models have been proposed, with evidence presented supporting each. Here, we review the current knowledge on the regulation of melanin exocytosis, internalization, processing, and polarization. Regarding the different transfer models, we discuss how these might co-exist to regulate skin pigmentation under different conditions, i.e., constitutive and facultative skin pigmentation or physiological and pathological conditions. Moreover, we discuss recent evidence that sheds light on the regulation of melanin exocytosis by melanocytes and internalization by keratinocytes, as well as how melanin is stored within these cells in a compartment that we propose be named the melanokerasome. Finally, we review the state of the art on the molecular mechanisms that lead to melanokerasome positioning above the nuclei of keratinocytes, forming supranuclear caps that shield the nuclear DNA from UV radiation. Thus, we provide a comprehensive overview of the current knowledge on the molecular mechanisms regulating skin pigmentation, from melanin exocytosis by melanocytes and internalization by keratinocytes to processing and polarization within keratinocytes. A better knowledge of these molecular mechanisms will clarify long-lasting questions in the field that are crucial for the understanding of skin pigmentation and can shed light on fundamental aspects of organelle biology. Ultimately, this knowledge can lead to novel therapeutic strategies to treat hypo- or hyper-pigmentation disorders, which have a high socio-economic burden on patients and healthcare systems worldwide, as well as cosmetic applications.

A conformational change of C-reactive protein in burn wounds unmasks its proinflammatory properties

Tissue damage in burn injury leads to a rapid increase of leukocytes and acute phase reactants. Plasma levels of C-reactive protein (CRP) rise within hours after the insult. No deficiency of this protein has been reported in humans, suggesting it plays a pivotal role in innate immunity. CRP in circulation is composed of five identical subunits [pentameric CRP (pCRP)]. Recently, deposits of structurally modified CRP (mCRP) have been found in inflammatory diseases. Little is known about this structural change and how it affects CRP functions. We analyzed CRP deposits in burn wounds and serum by immunohistochemistry, western blot and dot blot analysis. CRP was deposited in necrotic and inflamed tissue, but not in adjacent healthy tissue. Tissue deposited CRP was detected by mCRP-specific antibodies and structurally different from serum pCRP. mCRP but not pCRP induced reactive oxygen species production by monocytes and facilitated uptake of necrotic Jurkat cells by macrophages. In addition, it accelerated migration of keratinocytes in a scratch wound assay. The structural changes that occur in pCRP upon localization to damaged and inflamed tissue in burn wounds result in a functionally altered protein with distinct functions. mCRP exhibits opsonic, proinflammatory and promigratory properties which modulate wound healing.

Reappraisal of in situ immunophenotypic analysis of psoriasis skin: interaction of activated HLA-DR+ immunocompetent cells and endothelial cells is a major feature of psoriatic lesions

Psoriasis is an inflammatory skin disease of unknown aetiology. Many observations indicate that T cells play an important role in the pathogenesis of the disease. Upregulation of MHC class-II molecules on immunocompetent cells, endothelial cells and keratinocytes on lesional psoriatic skin has been regarded as a hallmark of the disease. However, there is some controversy in the literature regarding the cell types expressing class-II molecules and there is limited information about the presence of immune cells other than T cells and antigen presenting cells in the cellular infiltrates of psoriatic skin. We therefore reinvestigated the subject using immunocytochemical single and multiple staining techniques. In agreement with earlier reports, our studies showed that the cellular infiltrates in lesional skin consist largely of HLA-DR+/IL-2R+ T cells, HLA-DR+/CD1a+ Langerhans cells, and HLA-DR+/CD68+ macrophages. We found increased HLA-DR expression mostly on immuno-competent cells and endothelial cells, but no prominent HLA-DR expression on keratinocytes in lesional psoriatic skin. Upregulation of HLA-DR on endothelial cells and in mononuclear infiltrates was also evident in the non-lesional skin of psoriatic patients as compared with normal controls. B cells and natural killer cells were also found in the cellular infiltrates in lesional psoriatic skin. In spite of the presence of a large amount of activated T cells in the epidermis, we found that HLA-DR expression on keratinocytes was not a major feature of psoriatic skin.

IgG Fc receptor heterogeneity in human peripheral nerves

The presence of Fc-receptors for IgG, FcRI (CD64), FcRII (CD32) and FcRIII (CD16) in human peripheral nerves was studied by indirect immunofluorescence staining of cryostat sections with monoclonal antibodies (mabs). The mabs 32.2 against FcRI, IV.3 and C1KM5 against FcRII, B1D6 against a 40 kD FcR with low affinity for IgG, and Leu-11b and 3G8 against FcRIII stained a few scattered cells in the endoneurium, apparently monocytes/macrophages. In addition, B1D6 and Leu11b gave a membranous staining of Schwann cells, endothelial cells and perineurial cells. Axons and fibroblasts were not stained by any of the mabs. The FcR may be important in binding immune complexes, in phagocytosis, in the release of lymphokines as well as cytotoxic and inflammatory mediators and in local immunoregulation.

Properties of solubilized Fc gamma-receptors from psoriatic scales

Extracts from psoriatic scales, prepared using Tris-HCl buffer containing ethylenediaminetetraacetatic acid (EDTA) and 2-mercaptoethanol (ME), agglutinated erythrocytes (E) sensitized with IgG antibodies (A) (EA), but not E or E sensitized with F(ab')2-fragments of IgG. The agglutination was inhibited by IgG and Fc fragments of IgG, but not by IgA, IgM or F(ab')2-fragments of IgG. Partially reduced and alkylated IgG did not inhibit the agglutination, indicating that an inter-heavy-chain disulphide-linked Fc region is required for binding of FcR. The extracts inhibited EA, but not E or EAC rosette formation with mononuclear cells. The results strongly indicated that the extract contained functionally active FcR. The agglutinating activity of the extract was not affected by treatment with periodic acid or formaldehyde, whereas heat reduced the activity. Using a monoclonal antibody (B1D6) a functionally active 40 kDa FcR with low affinity for native IgG was purified from the scale extract. The extracts also contained FcR activity not recognized by B1D6.

Receptors for immunoglobulin G demonstrated on human peripheral nerve fibres by electron microscopy

The localization of class III of receptors for the Fc (fragment-crystallizable) region of immunoglobulin G (IgG) (Fc gamma RIII) on human peripheral nerve fibres was investigated by indirect immunoperoxidase staining of frozen nerve sections with the monoclonal antibody anti-Leu-IIb. Transmission electron microscopy revealed that Fc gamma RIII are localized to the entire surface membrane of the Schwann cell. Myelin and axons were not stained. Fc gamma RIII on human Schwann cells may be of significance in binding immune complexes, in phagocytosis, in release of lymphokines as well as cytotoxic and inflammatory mediators and in local immunoregulation.

In situ localization of interferons in psoriatic lesions

An indirect immunofluorescence technique, using murine monoclonal antibodies (MoAbs) against human IFN-alpha and human IFN-gamma was used to study IFNs in cryostat sections from psoriatic skin lesions. The IFNs were more pronounced in sections from highly active psoriasis than in sections from stationary psoriasis. In highly active psoriatic lesions IFN-alpha was localized to keratinocytes is stratum basale, to some epidermal dendritic cells, probably Langerhans cells, and to some mononuclear cells in dermis. IFN-alpha was usually not detected in sections from stationary psoriasis. IFN-gamma was localized to stratum corneum, to keratinocytes around microabcesses and to mononuclear cells in the dermal cell infiltrates, predominantly in highly active psoriatic lesions. Both IFN-alpha and IFN-gamma were localized to some endothelial cells in the papillary dermis. The MoAbs did not stain sections from unaffected skin from patients with psoriasis or sections from healthy individuals. The findings indicate that the IFN system in the skin may be of significance in the pathophysiology of psoriasis.