Pyrethrum is prepared from the flower of the pyrethrum plant, a member of the ragweed family, and is widely used as an in­secticide. It may act as an irritant or as a specific allergen. People who are allergic to ragweed may experience allergic symptoms when exposed to pyrethrum.

(egg-free, gluten-free, milk-free, wheat-free) 1/4 cup sugar 3 xups Rice Chex or Corn Chex 1 teaspoon cinnamon cereal 3 tablespoons milk-free margarine Mix sugar and cinnamon and set aside. Melt margarine in a frying pan over low heat and add cereal, stirring gently until each piece is coated. Sprinkle half the cinnamon-sugar mixture evenly over cereal, stirring to coat each piece. Continue heating, stirring, and sprinkling until all pieces are covered. Spread to cool before serving.

(gluten-free, milk-free, wheat-free)

Prepare mashed potatoes as directed, substituting water for milk. Slowly add beaten egg yolks to potatoes. Add crab and cayenne. Beat egg whites until stiff and then fold into potato mixture. Put in souffle dish or 1 V2 -quart casserole. Bake in 350° F oven for 50 minutes or until golden brown. Serves 6. Spicy Mashed Potatoes (gluten-free, milk-free, egg-free, wheat-free)

Combine all ingredients and serve at once. Serves 4

Feathers are a common cause of respiratory allergies. Aged feathers, in contrast to fresh feathers, appear to be more allergenic, which suggests that the allergens responsible for the symptoms are products that degrade. The most common source of exposure to feath­ers at home is pillows. Other sources are mattresses, cushions, and upholstery. A patient who is allergic to one type of feather is usually allergic to other types. People sensitive to feathers do not experience allergic reactions from egg-containing vaccines unless they are also allergic to egg protein.

Penicillium are fungi that belong to the class Fungi I: perfecti. These fungi are a common cause of rot in storage grain a in fruits and vegetables; they are also often found in houses, especia in their basements. Penicillium can produce allergic symptoms su as hay fever and asthma in allergic patients. See also Fungi; Molds.

Foods are intimately related to human existence, both physiologically and psychologically. For these reasons, it is under­standable that people tend to associate food with a wide variety of manifestations of diseases. Foods may cause adverse reactions through a variety of mechanisms such as allergic reactions, contaminants that cause toxic reactions or infections, food intolerance, and psychologi­cal mechanisms. The term food allergy is frequently misused by both people and physicians in referring to a variety of symptoms ranging from true allergies to vague, common complaints such as fatigue, tension, low energy, and headaches. Loose application of the word allergy to food has rendered the term almost useless in describing allergies that may or may not be related to the intake of food. Un­equivocal clinical symptoms produced by foods are uncommon; per­haps less than 1 percent of infants exhibit allergy to cow’s milk, and this may be one of the more common examples. Although foods may be important in cases of infantile eczema, urticaria, or anaphylaxis, they are relatively unimportant in most cases of allergic conjunctivitis, rhinitis, and asthma. Immunological reactions to foods are commonly divided into two groups, allergic (IgE) mediated and nonallergic mediated. The aller­gic mediated reaction is more common in children than in adults. Symptoms usually appear a few minutes to a few hours after inges­tion of the food, and they may be manifested by hives, angioedema, rash, asthma, abdominal symptoms such as diarrhea, vomiting, or abdominal pain, as well as by other anaphylactic symptoms. In clear-cut cases of food allergy, skin tests by the prick method are usually positive for the foods in question. In a recent study involving more than one hundred infants and children, the following foods were found to be important causes of symptoms: soybean, cow’s milk, peanuts and other nuts, and eggs. Nonallergic mediated reactions are reactions to foods that are me­diated by other immunological mechanisms. Symptoms are malab­sorption in the gastrointestinal tract, a disease of the intestines in which protein is lost; vomiting; and chronic diarrhea, among others. Respiratory symptoms such as pneumonia, cough, or asthma, and skin blemishes such as hives or angioedema may also appear. Symp­toms occur several hours to a few days after the food is eaten, in contrast to a few minutes to a few hours in the case of allergic (IgE) reactions. This delay makes it more difficult to establish an associa­tion between the symptoms and the food taken. Cow’s milk is the food most often responsible for such reactions; usually it causes primarily gastrointestinal and respiratory symptoms.

A cascade reaction is a series of reactions, such as that of the serum complement system, in which the reaction of the first component triggers the reaction of the next component, and so on, until all components of the system have reacted.

Antibodies belong to a group of proteins called immunoglobulins (abbreviated Ig) found in serum and other body fluids. An antibody is an immunoglobulin that reacts with a given antigen. For example, an Ig that binds ragweed pollen antigen is an antiragweed-pollen antibody. To understand how antibodies function, we must first un­derstand their structure. Like all proteins, immunoglobulins are made up of smaller units called amino acids. Twenty different amino acids are found in most proteins. These amino acids are linked by peptide bonds, forming either short or long chains called, respectively, oligo­peptides or polypeptides. Some proteins, including Ig molecules, con­sist of several polypeptide chains held together by other types of chemical bond. The polypeptide chains in a molecule usually are twisted around each other, giving the molecule the appearance of being round or ovoid. The final shape is one of the factors that deter­mines a protein’s function. This shape, in fact, is determined by the particular linear sequence of amino acids in the polypeptide chains that make up the protein molecule. The information that determines the amino-acid sequence of every protein the body makes is encoded in the DNA (deoxyribonucleic acid) of the genes of each cell in the body. Translation of this infor­mation begins in the nucleus of a cell. The amino acids are joined together one after the other, beginning at what is called the amino terminal end of the molecule and proceeding to the carboxyl terminal end. One of the most exciting avenues of research today is the search for the mechanism that controls the sequence of amino acids in the antibody molecule. The complexity of antibody structure makes it apparent that a complex mechanism is involved. The best-known fact about the structure of antibodies is that, in contrast to most other proteins, antibodies do not consist of a uni­form set of molecules. An antibody actually is a set of molecules that differ in a number of ways but which bind to the antigen that induced their synthesis. The key to understanding the heterogeneity of an antibody was discovered in investigations of the structure of a spe­cial type of immunoglobulin called myeloma protein. Sometimes, in both humans and other animals, tumors of plasma cells, called plas­macytomas, cause a disease called multiple myeloma. Apparently, all the plasmacytoma cells in an individual suffering from multiple myeloma arise from a single plasma cell that somehow was trans­formed into a tumor cell. This tumor cell, along with its progeny, synthesize only one type of Ig molecule. Because the cells secrete this molecule into the serum in great abundance, it is possible for scientists to separate the myeloma immunoglobulin from a person’s serum and subject it to a purification process, which continues until the serum is free of other proteins. The complete sequence of amino acids, as well as a three-dimensional structure of many of these mye­loma proteins, has now been determined. Fortunately, the structure of the myeloma Ig turns out not to be different from the structure of the normal Ig—that is, the normal antibody. From this research five major classes of immunoglobulin have been isolated: IgA, IgD, IgE, IgG, and IgM. Immunoglobulin G, pres­ent in the highest concentration in serum, has been studied the most extensively. Its structure serves as a model of the other classes of immunoglobulin. The IgG molecule shown in Figure 5.3 contains four polypeptide chains, two identical, heavy (or H) chains, and two iden­tical, light (or L) chains. Each half of the molecule contains an.H and an L chain. The chains are held together by an amino-acid bond (cysteine) on each chain. The weight of the molecule is about 160,000 daltons, one dalton being a unit of mass equal to one-sixteenth of an oxygen atom. The immunoglobulins IgD and IgE have the same four-chain structure. Serum IgA, however, may occur in the same monomeric form, or it may consist of two more units (dimer or polymer) held together by additional interchain bonds. In cer­tain secretions—for example, tears and saliva—IgA occurs in high concentrations. Here, it consists of two basic units joined by a small polypeptide chain called a secretory piece. IgM consists of five of the basic four-chain units joined by another small polypeptide known as a J chain. Its molecular weight is about 900,000 daltons, hence the name macroglobulin. As shown in Figure 5.3, each H or L chain is looped on itself in regions called domains, with four or five in an H chain and two in an L chain. In the IgG molecule, the first domain of each L chain lies opposite the first domain of its adjacent H chain; the same is true of the second domain of each chain. The third domain of an H chain is opposite the third domain of the other chain; this is also true of the fourth domain of each chain. Thus each IgG molecule has six pairs of overlapping domains, small globules within the larger IgG molecule. The first domain of a chain occurs at its amino terminal end, that is, the end synthesized first. Analysis of the amino-acid sequence of a large number of Ig molecules reveals much more sequence varia­bility in the first 110 amino-acid positions, beginning at the amino terminal end, of both the H and the L chains, than in the rest of the molecule. For this reason, this part of the polypeptide chains is called the variable (V) region. The rest of the molecule is the constant (C) region because there is much less variability when many Ig molecules are compared. The V and С regions of an L chain are of approxi­mately equal length, whereas the V region comprises only 20 to 25 percent of the length of the H chain. The heterogeneous nature of the sequence in each V region is most evident in three or four subre gions, each of which contains ten to twelve amino acids. These regions are called hypervariable (hv) regions. Because of the folding of the polypeptide chains in the V regions of the amino terminal H and L domains, the hv regions of each chain are extremely close to each other. In fact, they are situated in a cleftlike pocket near the amino terminal end of each half of the molecule. It is in this cleft that the antigenic determinant of an antigen molecule binds to an antibody molecule; hence, it is called the antigen-binding site of the Ig molecule. There are two identical antigen-binding sites on each IgG molecule; an IgM molecule has ten such sites. It is the particular amino acid sequence in the hv regions of a particular Ig molecule that is responsible for the unique configuration of its combining site; this configuration imparts speci­ficity to the Ig molecule and determines its affinity for its homologous antigen. It has been estimated that a human can synthesize more than a million different combining sites, or unique antibody molecules. Additional heterogeneity becomes apparent when the amino acid sequences of the constant regions are considered. These regions (about one hundred residues long in the L chain and three hundred to four hundred residues long in the H chain) are only relatively constant when different molecules are compared. Nevertheless, except for small differences due to genetic polymorphisms, it is possible to place the C-region sequences in a small number of major groups, two for the L chain (kappa and lambda) and five for the H chain (alpha, delta, epsilon, gamma, and mu). These differences in H-chain sequence are what distinguish the five classes of immunoglobulin. The differences in sequence are also responsible for differences in the function of the major classes of immunoglobulin. For example, IgE is the immunoglobulin respon­sible for allergic reactions. Within these classes, smaller variations in C-region sequences define Ig subclasses. For instance, there are four subclasses of IgG in humans:
IgGl, IgG2, IgG3, and IgG4. To a certain extent, these subclasses differ in their properties. Because no subclasses of IgE have been identified thus far, researchers believe that all IgE molecules have an equal effect in mediating an allergic reaction. Also of interest are the patterns of Ig classes that occur in various immune responses. Usually, IgM antibodies predominate in a primary immune response. In most secondary responses, IgG anti­bodies predominate, but smaller amounts of IgA and IgM antibodies are also produced. Some infectious diseases cause antibodies —mainly IgM—to be produced, whereas other diseases induce the production primarily of IgG antibodies. IgA antibodies predominate in most ex­ternal secretions. IgD antibodies are located on the surface of В lymphocytes; very little ever appears in serum. The production of IgE antibodies seems to be favored when the antigen dose is extremely small, when the dose is absorbed via the respiratory or gastrointestinal tract, or when, in experiments with animals, it is injected after adsorp­tion on alum. To recapitulate, antibody is produced by sets of lymphocytes in response to a specific stimulus, or antigen. Antibodies are capable of binding the antigens that induced the formation of the antibodies. An antibody, in fact, is a collection of different protein molecules, all of which can bind the same antigen. All antibodies belong to the group of serum proteins called immunoglobulins. Only when an immunoglobulin is known to bind a particular antigen is it referred to as an antibody against that antigen, and only a small proportion of the total immunoglobulin in serum can be associated with specific antibody activity; the remainder must be regarded as nonspecific, al­though antigens probably exist with which it will react. There are five major classes of immunoglobulin. An antibody against a given antigen usually contains immunoglobulins that belong to more than one of the five classes, and various antibody pools con­tain different proportions of each immunoglobulin. An antibody of each class has a different set of functions. The principal function of most antibodies is to resist infection; antibodies, however, may also be involved in a pathological reaction —for example, in an allergy.

Cover and simmer prunes in water until tender. Drain and cut up prunes, reserving liquid. Combine sugar, citric acid crystals, and rice flour. Gradually stir in liquid from prunes (about 1/2 cup). Cook and stir until slightly thickened. Add cut-up prunes and heat thoroughly. Sprinkle liver with salt. Brown on both sides in lamb drippings (about 2 minutes on each side). Serve with prune sauce. Serves 3.