Macrophages, but Not Langerhans Cell-like Cells of Dendritic Lineage, Express the CD36 Molecule in Normal Human Dermis: Relevance to Downregulatory Cutaneous Immune Responses?

Abstract

The CD36 molecule has been shown to be associated with subsets of peripheral blood monocyte/macrophages and, in cells isolated from either ultraviolet (UV)-irradiated or diseased skin, to induce downregulatory immune responses. Although macrophages are certainly present within normal human dermis, whether they normally express CD36 is still a matter of debate. In this study, we investigated dermal CD36-expressing macrophages in situ using the gold immunoelectron microscopic technique on tissue ultracryosections. This is a very sensitive and specific method, and its results clearly reflect the in vivo immunophenotypic constitutive situation. Macrophages in normal human dermis were variously shaped from round to dendritic and were localized either immediately beneath the epidermis, in perivascular areas, or in intervascular zones. Macrophages showed consistent gold-positive staining on their cell surface. In contrast, other dermal cells, including fibroblasts, lymphocytes, and mast cells, as well as dermal fibers, were not decorated with gold; dermal Langerhans cell-like dendritic cells (LC/DC), though they did show gold labeling in some intracytoplasmic organelles, did not show any gold particles along their plasma membranes. Therefore, although macrophages in normal human dermis exhibit variability with regard to their localization and shape, they regularly and constitutively expressed CD36. CD36 molecules may be considered a useful marker for macrophages in normal human dermis and may furthermore confer on macrophages, or a subpopulation thereof, intriguing functional properties (e.g., downregulatory capacity versus upregulatory capacity subserved by LC/DC) within the cutaneous immune system.

Keratinocytes constitutively express the CD95 ligand molecule on the plasma membrane: an in situ immunoelectron microscopy study on ultracryosections of normal human skin

“…They showed gold granules scattered not only within the cytoplasm, but also along the plasma membrane (Fig. 1), because the UCMT/IEM technique is known to reveal clearly the antigenic moieties localized in the whole surface of a tissue section 14–17,22 …”

“…The UCMT technique herein used was similar, with minor changes, to that reported previously 16 . Briefly, biopsies were immediately immersed in paraformaldehyde 2% in 0·1 mol L −1 phosphate buffer, pH 7·4.…”

“…Such a technique, in fact, closely reflects the in vivo situation because slightly fixed tissues are cut immediately without any embedding; 14,15 UCMT/IEM, in addition, shows both an excellent specificity because the precise antigenic location (e.g. cytoplasm vs. cell surface) is recognized, and a superior sensitivity because even minimal antigenic amounts can be detected 16,17 …”

Role of Macrophages in the Pathogenesis of Atopic Dermatitis

“…Healthy human skin macrophages are known to express CD36, and functionally CD36 is linked to phagocytosis of apoptotic cells [19, 20]. …”

Leprosy: accessory immune system as effector of infectious, metabolic, and immunologic reactions

“…Type 1 or factor XIIIa+ dendrocytes predominate in the papillary and subpapillary dermis or around venules; as components of the so‐called dermal microvascular unit, these cells may associate with endothelial cells, pericytes, mast cells, and CD4+ and CD8+ lymphocytes to form functionally complex vascular cuffs. Their cytoplasm is characterized by the ‘‘a’' subunit of a fibrin‐sensitive coagulation proenzyme; 101–112 they may engulf small particles (charcoal, melanin, hemosiderin, lipids), but phagolysosomal activity is absent. Electron microscopy studies show pinocytic vesicles and plaque‐like thickening of the plasma membrane, with surface fibrils called fibronexuses and soluble organic matter absorption potential 113,114 (Fig.…”