Basophilic substance

Basic dyes such as methylene blue or toluidine blue are positively charged at the pH of most staining solutions used in histology. Thus the dyes bind to acidic (i.e., those that become negatively charged on dissociation of a proton) substances in the cell. These acidic molecules are therefore referred to as basophilic substances. Give some examples of basophilic substances. 

Histamine is a substance present in various tissues of die body, such as die heart, lungs, gastric mucosa, and skin (Pig. 36-1). The highest concentration of histamine is found in die basophil (a type of white blood cell) and mast cells diat are found near capillaries. Histamine is produced in response to injury. It acts on areas such as die vascular system and smooth muscle, producing dilatation of arterioles and an increased permeability of capillaries and venules. Dilatation of die arterioles results in localized redness. An increase in die permeability of... 

This chapter highlights the mechanisms responsible for mast cell activation during anaphylactic responses to environmental substances. In addition to discussing in detail the activation of mast cells and basophils by IgE and antigen, we also will describe how mouse models have been used to analyze the importance of various proteins, cells, mediators and activation mechanisms in the expression of anaphylaxis in that species. 

C3a and C5a are released into the fluid surroundings where they serve as potent anaphylotoxins in that they cause vasoactive substances such as histamines to be released from mast cells and basophils. C5a is also strongly chemotactic for neutrophils. 

Basophils are the least abundant of the leukocytes and account for less than 1% of the total number of white blood cells. They are similar structurally and functionally to the mast cells found in connective tissues, especially in the lungs, skin, and gastrointestinal tract. Basophils and mast cells play an important role in allergic reactions. The granules of these cells contain many substances, including ... 

Histamine, an important mediator (local signaling substance) and neurotransmitter, is mainly stored in tissue mast cells and basophilic granulocytes in the blood. It is involved in inflammatory and allergic reactions. Histamine liberators such as tissue hormones, type E immunoglobulins (see p. 300), and drugs can release it. Histamine acts via various types of receptor. Binding to Hi receptors promotes contraction of smooth muscle in the bronchia, and dilates the capillary vessels and increases their permeability. Via H2 receptors, histamine slows down the heart rate and promotes the formation of HCl in the gastric mucosa. In the brain, histamine acts as a neurotransmitter. 

Immunoglobulins can also be receptors. For example, molecules of IgE bound to basophils and the related mast cells of tissues serve as receptors for allergens. Binding of an allergen to the IgE molecules stimulates the release of granules containing histamine and other substances (Chapter 31). 

Eosinophils are attracted by proteins released by T cells, mast cells and basophils [eosinophil chemotactic factor of anaphylaxis (ECF-A)]. They bind schistosomulae coated with IgG or IgE, degranulate and release major basic protein, which is toxic. Eosinophils also release histaminase and aryl sulfatase, which inactivates histamine and Slow reacting substance of anaphylaxis (SRS-A). This results in antiinflammatory effects and inhibits migration of granulocytes to the site of injury. 

As mentioned earlier, one of the principal mediators involved in certain allergic reactions (e.g., type I anaphylactic) is histamine. Histamine is an endogenous substance that is synthesized, stored, and released primarily from tissue mast cells and circulating basophils. The actions of histamine are mediated by at least three distinct receptor subgroups Hl5 H2, and H3. Of these, Hj receptors mediate the major actions in humans related to allergic responses. A list of some of the principal actions of histamine in humans is shown in Table 7.4. 

Neutrophils form 60-70% of the leucocytes in blood. They are phagocytic and their function is to remove debris and infectious particles. Eosinophils are also phagocytic and form 1 -4% of white cells. They are involved in defence against parasites and in allergic responses. Basophils form 0.5% of leucocytes, are phagocytic and release histamine and other substances involved in allergic responses. 

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