Latin name: Zea mays
Source material: Pollen
Family: Poaceae (Gramineae)
Sub family: Panicoideae
Common names: Maize, Corn
Maize/Corn pollen (Zea mays) g202 must be differentiated from Maize/Corn (Zea mays) f8, the food.
A grass species producing pollen, which may induce hayfever, asthma and conjunctivitis in sensitised individuals.
Maize is a tropical grass belonging to the Panicoideae subfamily. The original habitat is uncertain; it was probably South America or Mexico. The plant is now grown in most places in the world where summers are reasonably warm. Corn is one of the most commonly grown foods. It is the staple cereal of the human diet in Central America and tropical South America, and in many parts of Africa. It is extremely important in livestock rearing, food processing and other commercial activities in developed countries.
The plant is a single-stemmed annual, grown from one seed, though sucker shoots (which may produce seed) rise from the base. The single stalk, terminating in the tassel or staminate flowers, can grow to over 3m, at a fast rate. The smooth leaves, usually drooping and usually green, may be over half a metre long.
The flowers are monoecious (individual flowers are either male or female, but both sexes can be found on the same plant) and are pollinated by wind. The female flowers are borne on a receptacle, termed the ‘ear’, which arises at a leaf axil near the mid-point along the stem. Normally one to three or more such ears develop. The flower organs, and later the grain kernels (in more or less longitudinal rows), are enclosed in several layers of papery tissue, termed husks. Strands of ‘silk’, actually the stigmas from the flowers, emerge from the terminals of the ears and husks at the same time that the pollen from the terminal tassels is shed. In the Northern Hemisphere Maize is in flower between July and October, and the seeds ripen between September and October. The grains vary in size, shape, and colour.
Sweet corn is distinguished from field corn by the high sugar content of the kernels at the early "dough" stage, and by wrinkled, translucent kernels when dry.
The plant is found in cultivated beds, and does not grow wild except in a very limited way, when escaping cultivation.
Maize is eaten straight off the cob or processed in a variety of ways.
Maize pollen may be used in herbal therapies. The stalks, cobs, grains and oil have many agricultural and industrial uses.
Zea m 1, a group 1 grass allergen, an expansin (1-9).
Zea m 2, a group 2 grass allergen (10, 11).
Zea m 3, an expansin (12).
Zea m 4, a group 4 grass allergen, a pectate lyase (8, 9, 13).
Zea m 5, a protein with unknown biological function (14).
Zea m 7, a calcium binding protein (15, 16).
Zea m 11, a trypsin inhibitor, found in the pollen and seed (10, 17).
Zea m 12, a profilin, an actin-binding protein (1, 9, 18, 19).
Zea m 13, a 50 kDa protein, a group 13 grass allergen, a polygalacturonase (20-24).
Zea m Zm13, an Ole e 1-related protein (Olive tree pollen allergen) (22, 24-26).
The Group 5 allergen (Zea m 5) is inferred as a result of cross-reactivity studies (see below).
Zm13, an allergen having significant sequence homology with a number of pollen- or anther-specific proteins from monocot and dicot plants, as well as with recently described allergens from Olive and Rye grass, has been isolated. The recombinant Zm13 fusion protein reacted with serum IgE from grass pollen-allergic patients, indicating that Zm13 and homologous proteins represent a family of conserved plant allergens (22).
Extensive cross-reactivity among the different individual species of the genus may be expected (as well as among members of the family Poaceae, to a certain degree), and is especially likely among Bahia grass (g17), Johnson grass (g10) and Maize pollen (g202), related through the sub-family Panicoideae (27, 28).
Cross-reactivity between grass and maize pollen extracts has been studied by different authors using the RAST inhibition test. Most of them showed a low degree of reactivity (9, 14, 29). In addition, others reported that many patients with pollinosis showed positive skin-prick tests to maize pollen but not to grasses, while others had positive tests to grass pollens but not to maize pollen (43).
The structural differences found in maize and other grass species reflect the fact that maize belongs to the Panicoidae, while European native grasses belong to the same grass sub-family, Pooideae (30).
As a result of the presence of allergens belonging to group 1, 2, 4 and grass allergen families, varying degrees of cross-reactivity between maize pollen and grass pollen are possible, but have not been extensively studied or reported on. Similarly, the calcium binding protein and profilin may also contribute.
Maize pollen contains one of the Group 1 allergens, which are glycoprotein isoallergens shared by many species of grass (31). Group 1 allergens are highly homologous, but not all of the antigenic epitopes are crossreactive (32). For example, Group 1 allergens from eight different clinically important grass pollens of the Pooideae (Rye grass, Canary grass, Meadow grass, Cocksfoot and Timothy), Chloridoideae (Bermuda grass) and Panicoideae (Johnson grass, Maize) were isolated, and IgE binding to an allergic human serum pool was conducted to determine the degree of antigenic and IgE-binding similarities. The highest IgE-binding similarity was observed between Cocksfoot and Rye grass (53%) and between Rye grass and Canary grass (43%). No IgE-binding similarity was observed between Maize and other grasses. The highest antigenic similarity was also observed between Rye grass and Cocksfoot grass (76%), and the lowest similarity between Rye grass and Maize (23%) and Rye grass and Bermuda (10%) (33).
Highly homologous Group 1 allergens have been demonstrated between Pha a 1 from Canary grass pollen, Lol p 1 from Rye grass pollen (a deduced amino acid sequence identity of 88.8%), Hol l 1 from Velvet grass pollen (88.1%), and Phl p 1 from Timothy grass pollen (86.6%) (34). The major Timothy grass pollen allergen Phl p 1 also cross-reacts with most grass-, Corn-, and monocot-derived Group 1 allergens (35). Monoclonal antibodies of Cyn d 1 (Bermuda grass) recognised cross-reactive epitopes on proteins from 8 other grasses including Rye grass, Timothy grass, Meadow grass and Johnson grass (36).
However, other studies have found greater similarity between Zea m 1 from Maize pollen and individual grasses. Zea m 1 and Zea m 13 have been reported to have higher sequence identities: 72% and 70% to the corresponding Phl p 1 and Phl p 13 allergens of Timothy grass pollen respectively (12). Zea m 1 and Zea m 13 have been reported to have a high IgE prevalence in the population groups studied, and are reported to be responsible for cross-reactivity to grasses growing in temperate climate zones (12).
For example, in an Australian study, 29 of 34 (85%) consecutive patients presenting with grass pollen allergy were skin-prick test positive to Bahia grass pollen. Pas n 1 from Bahia grass was shown to have sequence homology with other group 1 grass allergens, and is more closely related to the maize pollen group 1 allergen (85% identity) than to ryegrass Lol p 1 or Timothy grass Phl p 1 (64% and 66% identity respectively) (37). This would indicate that cross-reactivity between Maize pollen Zea m 1 and other grasses is highly variable, and may be high with specific grasses rather than grasses in general.
It appears that Maize pollen also contains a Group 5 allergen. Almost 90% of grass pollen-allergic patients are sensitised against Group 5 grass pollen allergens. A monoclonal human IgE antibody has been shown to cross-react with Group 5A isoallergens from several grass and Corn species (38). Polymorphic forms of Pha a 5 from Canary grass have been shown to share significant sequence identity with other Group 5 allergens from Rye grass, Timothy and Meadow grass pollens (37).
The cross-reactivity of IgE antibodies to Group 1 and Group 5 allergens has been shown to be highly variable in eight grass pollen species. Cross-reactivity of IgE antibodies against Lol p I or Lol p V (both from Rye grass pollen) to Dactylis glomerata (Cocksfoot), Festuca rubra (Red Fescue), Phleum pratense (Timothy), Anthoxanthum odoratum (Sweet Vernal grass), Secale cereale (Cultivated Rye), Zea mays (Maize/Corn), and Phragmites communis (Common Reed) was investigated by means of RAST-inhibition. Within a group of sera the degree of cross-reactivity was demonstrated to be highly variable. Individual sera were not always equally cross-reactive to all pollen species. A high degree of cross-reactivity for Group 1 allergens did not necessarily imply the same for Group 5 allergens. Group 1 and Group 5 representatives were found to be present in all eight species (14). Zea mays may in fact not contain a Group 5 allergen, or a Group 2 allergen (9).
Although the profilin panallergen (Zea m 12) is present in Maize pollen and therefore cross-reactivity with other profiling-containing pollen may be anticipated, few studies have evaluated the clinical relevance of this allergen. A profilin with unknown allergenic potential has been isolated from Tomato, and shown to have a sequence similarity of 87% with profilins from tobacco, 78% with timothy grass, 77% with Arabidopsis profilin, 73% with birch profilin, and 77% with maize profiling (39). Rice profilin has an 89% similarity to maize profilin, 87% to Bermuda grass and 89% to Timothy grass profiling (40). Because of their fundamental role in the formation of the cytoskeleton, profilins are highly conserved proteins; however, profilin IgE reactivity is weak (IgE prevalence for Timothy pollen amounts to just on 10%) (22).
Group 13 allergens are detectable in all common grasses (Cynodon dactylon, Dactylis glomerata, Festuca pratensis, Lolium perenne, Phleum pratense, Poa pratensis, Secale cereale, Holcus lanatus, Hordeum vulgare and Zea mays), and show IgE cross-reactivity with each other. Protein sequencing clearly confirms structural identities between different grass species, although individual variations are found (21).
Zea m Zm13 shows significant sequence homology with a number of pollen- or anther-specific proteins from monocot and dicot plants, as well as with recently-described allergens from olive tree and rye grass pollen (22, 26).
IgE mediated reactions
Maize pollen is found in lower concentrations in aerobiological studies because of its density. Nevertheless, individuals exposed to this pollen may have asthma, allergic rhinitis and allergic conjunctivitis induced (41-43). Respiratory allergy is the most frequently produced by maize, and is associated more with the management of the grain than with its ingestion (44, 45). Although not many studies describing maize pollen allergy have been reported to date, anecdotal evidence suggests that maize pollen can often induce allergic symptoms.
Although maize pollen is abundantly produced, it is found in low concentrations as airborne pollen because of its weight. In fact, most maize pollen falls within 50-70 m from the source, so it has been widely assumed to be a minor agent of pollen allergy (46). However, it is possible that strong winds may carry maize pollen much further from source. A 55-year-old man was described who had a 16-year history of recurrent episodes of rhinoconjunctivitis and asthma during maize pollen season. He worked in a rural area where maize, fruit trees and vegetables were found in abundance. Prick tests were negative for a wide range of pollens and other aeroallergens, with the exception of maize pollen. Total IgE was 1751 lU/ml, and specific IgE to maize pollen was 4.28 kU/l. There was little cross-reactivity shown between maize and grass pollens in this patient (46).
In a study examining eustachian tube function in 80 Mexican patients with allergic rhinitis and 50 healthy controls, the most frequent skin test positivity was to Dermatophagoides (62%), Maize pollen (44%), and Cockroach (37%) (47).
In a study of 101 patients with asthma living in Comarca Lagunera, Spain, specific IgE-determination tests demonstrated that 57% of the group were sensitised to Maize pollen (41). Z. mays pollen was also shown by specific IgE tests to be an important pollen among 614 respiratory-allergic patients in Turkey (48).
An evaluation was carried out of sensitisation to pollens in 32 children under 8 years attending an allergy unit in Portugal, of whom 72% complained of symptoms of allergic rhinitis, 66% conjuntivitis, 50% bronchial asthma and 34% allergic rhinitis and bronchial asthma. All children were skin-prick test positive to grass pollens tested, and 38% were monosensitised. The order of frequency for grass pollen sensitization was Dactylis (94%), Hordeum (75%), Phleum (72%), Poa (69%), Avena (66%), Festuca (63%), Triticum (59%), Secale (53%), Lolium (50%) and Maize pollen (31%) (49).
In 468 asthmatic children in Johannesburg, South Africa, Maize/Corn pollen was among the most common allergens on specific IgE testing (50).
Thirty-three Navajo patients were seen in a private allergy consultation practice in Flagstaff, Arizona. Skin test and historical data were available from nine atopic patients to evaluate hypersensitivity reactions to oral corn pollen used in the Navajo ceremonials. Six of the nine patients had positive skin test reactions to Corn pollen, and four of these six reported symptoms from oral Corn pollen. The symptoms included various combinations of oral and ear itching, sneezing, cough, and wheezing (51).
It is important to differentiate symptoms from exposure to maize dust from those as a result of exposure to maize pollen. The dust of stored maize has been reported to be a cause of respiratory symptoms. During the storage process, maize corn dust may be contaminated by moulds and thermophilic actinomycetes. These may result in occupational hypersensitivity pneumonitis (52).
Compiled by Dr Harris Steinman, developer of Allergy Advisor, http://allergyadvisor.com
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