Il5

Expression of FceRI

High levels

High levels

Low levels (function unclear)

Major granule contents

Histamine, heparin and/or chondroitin sulfate, proteases

Histamine, chondroitin sulfate, protease

Major basic protein, eosinophil cationic protein, peroxidases, hydrolases, lysophospholipase

FceRI, Fee receptor type I; IL, interleukin.

FIGURE 19-2 Morphology of mast cells, basophils, and eosinophils. Photomicrographs of Wright-Giemsa-stained perivascular dermal mast cells (A, arrows), peripheral blood basophil (B), and peripheral blood eosinophil (C) are presented. Note the characteristic red staining of the cytoplasmic granules in the eosinophil and blue-staining cytoplasmic granules of the basophil. (A courtesy of Dr. George Murphy and B and C courtesy of Dr. Jonathan Hecht, Department of Pathology, Brigham and Women's Hospital, Boston, Massachusetts.)

FIGURE 19-2 Morphology of mast cells, basophils, and eosinophils. Photomicrographs of Wright-Giemsa-stained perivascular dermal mast cells (A, arrows), peripheral blood basophil (B), and peripheral blood eosinophil (C) are presented. Note the characteristic red staining of the cytoplasmic granules in the eosinophil and blue-staining cytoplasmic granules of the basophil. (A courtesy of Dr. George Murphy and B and C courtesy of Dr. Jonathan Hecht, Department of Pathology, Brigham and Women's Hospital, Boston, Massachusetts.)

Activated mast cells secrete a variety of mediators that are responsible for the manifestations of allergic reactions (Table 19-2). These include substances that are stored in granules and rapidly released upon activation, and others that are synthesized upon activation. The production and actions of these mediators are described later.

Different mast cell populations exist that are distinguished by their anatomic locations, granule contents, and activities (Table 19-3). In rodents, two major subsets of mast cells have been described, one found in the mucosa of the gastrointestinal tract and the other in connective tissues. The mucosal mast cells have abundant chondroitin sulfate and little histamine in their granules. The development of mucosal mast cells in vivo depends on the cytokine IL-3 produced by T cells. Mast cells may be cultured from rodent bone marrow in the presence of IL-3, and such cultured mast cells resemble mucosal mast cells on the basis of the high granule content of chondroitin sulfate and low histamine concentration. The human counterpart of mucosal mast cells is most often identified by the presence of tryptase and the absence of other neutral proteases in the granules. In humans, the mucosal type of mast cells predominates in intestinal mucosa and alveolar spaces in the lung, and their presence is also T cell dependent. Connective tissue mast cells, also first identified in rodents, are found in the lung and in the serosa of body cavities. Their major granule proteoglycan is heparin, and they produce large quantities of histamine. Unlike mucosal mast cells, connective tissue mast cells show little T cell dependence. In humans, the corresponding subset is identified by the presence of several neutral proteases in the granules, including tryptase, chymase, cathepsin G-like protease, and carboxypeptidase. Human connective tissue mast cells are found in the skin and intestinal sub-mucosa. Although the idea of these subsets has provided a valuable framework for studies of mast cells, it is clear that the populations are neither fixed nor clearly separable.

The locations, granule contents, and relative T cell dependence of different mast cell populations suggest that each may be important in a different set of disease processes. It is likely that mucosal-type mast cells are involved in T cell- and IgE-dependent immediate hyper-sensitivity diseases involving the airways, such as bronchial asthma, and other mucosal tissues. Conversely, connective tissue-type mast cells mediate immediate hypersensitivity reactions in the skin.

Basophils are blood granulocytes with structural and functional similarities to mast cells. Like other granulo-cytes, basophils are derived from bone marrow progenitors (a lineage different from that of mast cells), mature in the bone marrow, and circulate in the blood (Fig. 19-2B). Basophils constitute less than 1% of blood leukocytes. Although they are normally not present in tissues, basophils may be recruited to some inflammatory sites. Basophils contain granules that bind basic dyes, and they are capable of synthesizing many of the same mediators as mast cells (see Table 19-2). Like mast cells, basophils express FceRI, bind IgE, and can be triggered by antigen binding to the IgE. Therefore, basophils that are recruited into tissue sites where antigen is present may contribute to immediate hypersensitivity reactions.

Was this article helpful?

0 0
Dealing With Asthma Naturally

Dealing With Asthma Naturally

Do You Suffer From ASTHMA Chronic asthma is a paralyzing, suffocating and socially isolating condition that can cause anxiety that can trigger even more attacks. Before you know it you are caught in a vicious cycle Put an end to the dependence on inhalers, buying expensive prescription drugs and avoidance of allergenic situations and animals. Get control of your life again and Deal With Asthma Naturally

Get My Free Ebook


Post a comment