A fine structure study of some cellular components in allergic reactions. II. Mast cells in normal and atopic human skin

Mastocytosis and the skin

The most frequent site of organ involvement in individuals with any form of mastocytosis is the skin. Cutaneous lesions include urticaria pigmentosa, mastocytoma, diffuse and erythematous cutaneous mastocytosis, and telangiectasia macularis eruptiva perstans. The major histologic feature is an increase in the number of mast cells in the dermis. Treatment depends on the type of skin lesions.

Ultrastructural and Immunohistochemical Characterization of Normal Mast Cells at Multiple Body Sites

This article reviews the ultrastructural and immunohistochemical features of normal human mast cells (MC) at multiple tissue sites. Current literature indicates that granules containing discrete scrolls (scroll-rich morphology) are frequent in MC from bowel mucosa and lung, locations where the majority of MC show only tryptase immunoreactivity (MC(T)). In contrast, most MC from skin, breast parenchyma, axillary lymph nodes, and bowel submucosa are characterized by scroll-poor morphology (that is, granules are rimmed by incomplete scrolls forming parallel lamellae and containing central, amorphous granular material or grating/lattice-like structures) and show both tryptase and chymase immunoreactivity (MC(TC)). MC having granules with both scroll-rich and scroll-poor features can occur in all tissue sites, and an occasional MC, especially in lung and bowel, may show only chymase immunoreactivity (MC(C)). Chymase immunoreactivity in MC also is closely associated with avidin binding and carboxypeptidase reactivity. We conclude that there is ultrastructural and immunophenotypic diversity among normal human MC, although certain forms predominate in specific tissue environments. In skin, breast tissue, axillary lymph nodes, and bowel submucosa MC tend to have scroll-poor granules and stain for avidin, chymase, tryptase, and carboxypeptidase, whereas, in lung and bowel mucosa MC granules tend to be scroll-rich and stain only for tryptase with currently available reagents.

The Skin in Mastocytosis

The most frequent site of organ involvement in patients with any form of mastocytosis is the skin. Cutaneous expressions include urticaria pigmentosa, mastocytoma, diffuse and erythrodermic cutaneous mastocytosis, and telangiectasia macularis eruptiva perstans. The cutaneous lesions tend to appear early in life. Although urticaria pigmentosa has been reported in 12 pairs of twins and one set of triplets, the majority of affected individuals have no familial association. Most patients with systemic mastocytosis have skin lesions; however, an occasional patient will have systemic disease with no other skin features than flushing. In lesional cutaneous sites and in non-lesional skin, there is an increase in the number of mast cells. Electron microscopy shows quantitative differences between lesional skin mast cells from patients with and without systemic disease. The mast cells from adult patients with systemic disease have a larger mean cytoplasmic area, nuclear size, and granule diameter. The granules contain predominantly grating/lattice structures. The cutaneous mast cells contain tryptase and chymase. They retain their functional reactivities to relevant secretory stimuli, such as C3a, morphine sulfate, and calcium ionophore A23187. Lesional skin contains histamine, leukotriene B4, prostaglandin D2, 5-hydroxyeicosatetraenoic acid, platelet-activating factor, and heparin. Treatment of the cutaneous manifestations includes the use of H1 and H2 antihistamines, oral disodium cromoglycate, psoralens plus ultraviolet A photochemotherapy, and potent topical corticosteroid preparations.

Mast cells in cutaneous mastocytosis: accumulation of the MCTC type

Lesional (n = 15) and non-lesional (n = 10) skin of subjects with mastocytosis was analysed for the distribution and concentration of trypase positive, chymase negative mast cells (MCT) and tryptase positive, chymase positive mast cells (MCTC) cells and compared to normal skin (n = 23) and non-lesional skin of subjects with unexplained anaphylaxis or flushing episodes (n = 6). Skin biopsies were fixed in Carnoy's fluid and subjected to double immunohistochemical staining with biotinylated mouse monoclonal anti-chymase antibody followed by alkaline phosphatase-conjugated mouse monoclonal anti-tryptase antibody. MCTC cells were the only type of mast cells seen in all specimens analysed and in each case were more numerous in superficial compared to deep regions of dermis. The concentration (mean +/- s.d.) of mast cells in the superficial dermis of mastocytosis lesions (40 985 +/- 21 772 mast cells/mm3) was significantly increased over that in corresponding areas of non-lesional skin from subjects with mastocytosis (7178 +/- 3607 mast cells/mm3), skin from subjects with idiopathic anaphylaxis or flushing episodes (6974 +/- 3873 mast cells/mm3) and normal skin (7347 +/- 2973 mast cells/mm3). The exclusive presence of MCTC cells in skin lesions of mastocytosis which are characterized by non-malignant hyperplasia of mast cells suggests involvement of local tissue factors in mast cell recruitment and differentiation.

Reflections on the mechanism(s) of action of sodium cromoglycate (Intal) and the role of mast cells in asthma

In this review, only a few questions concerning the mechanism(s) of action of sodium cromoglycate in asthma have been considered. The large number of cells and mediator pathways where sodium cromoglycate may have pharmacological effects are depicted. In addition to its mast cell effect, sodium cromoglycate is also inhibitory to macrophages, eosinophils, monocytes and platelets, which are all important components in the inflammatory response of asthma. From studies with bradykinin and sulphur dioxide it is also known that the drug can block afferent discharges along non-myelinated nerves. Although the ability of sodium cromoglycate to block late phase responses and acquired hyper-reactivity is not questioned, to what extent its therapeutic efficacy can be accounted for by actions on these leukocytes and reflex pathways is not known. When administered to patients with asthma, sodium cromoglycate results in symptomatic improvement, but there is still much to be learned about its mode of action.

Ultrastructural changes in human skin mast cells during antigen-induced degranulation in vivo

Human skin mast cells were degranulated in vivo by intradermal injection of antigen. Biopsy specimens of control and stimulated skin were obtained at 5 minutes, again at 10 to 15 minutes, and analyzed by electron microscopy. Degranulation, defined as dissolution of granule contents and swelling in at least 20% of secretory granules of mast cells was observed in one third of mast cells at 5 minutes and in nearly two thirds of mast cells at 10 to 15 minutes, but was absent in biopsy specimens of control subjects. Anaphylactic degranulation was characterized by extensive fusion of granules to form degranulation channels, fusion of channels with the cell membrane to form large pores, and exocytosis of amorphous or fibrillar granule matrix into the connective tissue. Extruded secretory granules of skin mast cells persist for at least 15 minutes in the connective tissues, in apparent contrast to the process of in vivo degranulation in nasal and lung mast cells.

Ultrastructure of cerebellar capillary hemangioblastoma. V. Large pinocytic vacuolar bodies (megalopinocytic vesicles) in endothelial cells

Large pinocytic vacuolar bodies (megalopinocytic vesicles) containing electron-dense granulo-fibrillary material, not previously described in micro-vascular endothelium of brain tumors, were observed in endothelial cells of all five cases of cerebellar hemangioblastoma studied ultrastructurally. They were present in 23% of a total of 132 capillary profiles studied. Some were prominent and aggregated to occupy a large portion of the endothelial cytoplasm. Unlike the ordinary pinocytic vesicles in endothelial cells, they were distributed predominantly in the vicinity of the nucleus and surrounded by abundant organelles. They were irregular and usually several times larger than macropinocytic vesicles. The larger vacuolar bodies were often surrounded by bundles of microfilaments which often anchored on their limiting membrane. They coexisted frequently with Weibel-Palade bodies and occasionally fused with them. Convergence of coated vesicles and micropinocytic vesicles with the vacuolar bodies was present. However, there was no direct contact between the vacuolar bodies and Golgi apparatus, rough and smooth endoplasmic reticulum and mitochondria. The vacuolar bodies were closely associated with pericytic foot processes. It was suggested that they were formed by invagination of the abluminal cytoplasmic membrane with engulfed extracellular material and migrated internally. Discharge of their contents into the vascular lumen and interendothelial space was observed. Some had a disrupted membrane with a suggestion of release of contents into the cytoplasmic matrix. Their function is unknown, but they may serve as a specific vehicle of transport or digestive mechanism in microvascular endothelium under certain pathophysiological conditions, such as neoplasm, to meet the increasing metabolic demands.

The diversity of mast cell-derived mediators: implications for acute, subacute, and chronic cutaneous inflammatory disorders

The mast cell in tissues represents an effector cell capable of elaboration of all the essential mediators of inflammation. The effects of uncontrolled activation may be divided into pharmacologic and inflammatory phases with attendant implications for the initiation of both acute and subacute pathologic processes. The elaboration of chemical mediators by the mast cell makes it possible to recruit blood cells and proteins essential to host defense by a controlled physiologic process that can proceed without significant local tissue damage. When uncontrolled, the same potentiality can be injurious, with the nature of the clinical problem depending upon the location of the cells, the intensity of activation, and the ratio of newly generated and preformed mediators released. The evidence that the mast cell can participate in each form of immunologic reaction--immediate, immune complex, and delayed- as a primary or secondary effector cell and the diversity of its products foretell an evolving recognition of its role in host defense and tissue injury. It is pertinent to develop further methods and criteria to define the nature and extent of mast cell participation in disease processes.