Latin name: Paspalum notatum
Source material: Pollen
Family: Poaceae (Gramineae)
Sub family: Panicoideae
Common names: Bahia Grass, Bahiagrass, Paraguay Paspalum
A grass species producing pollen, which often induces hay fever, asthma and conjunctivitis in sensitised individuals.
There are over 300 species of bull grasses (genus Paspalum) found throughout tropical and warmer regions of both hemispheres, with about 50 species native or introduced into the United States (1). Bahia grass (P. notatum) is a perennial grass native to southern Brazil, Uruguay, northern Argentina, and north-western Paraguay, and is found in most Central and South American countries. It has been introduced as a turf and forage grass into East and West Africa, Australia, India, Japan, Mexico, and the southern and eastern United States, where it has become naturalised (1). A genus relative, Dallis grass (P. dilatatum), also native to South America, is found extensively throughout the south and southwest (1).
Paspalum notatum is a sod-forming, deep-rooted, warm-season, perennial grass. It spreads by short, stout, woody runners and by seed. The runners have many large, fibrous roots, which form dense, tough sods, even on drought-prone sandy soils. The leaf bases at the terminus of each rhizome usually have a purplish hue. The stems of P. notatum are ascending, usually ranging from 20 to 75cm tall, and the dark green leaves are 4 to 10mm wide and 6 to 25cm long.
The inflorescences have two to several spicate branches 4 to 12cm long, and each branch (or raceme) has two rows of spikelets, either paired, or positioned with one slightly below the other. Flowering is between June and November in the Northern Hemisphere. (Bahia grass ripens progressively over the summer in the United States, and the seed matures very quickly.) Besides vegetative spread, some varieties can reproduce asexually by unfertilised yet viable seeds; the sexually-reproducing varieties are wind-pollinated. The plant seeds prolifically during the summer.
Southern subtropical grasses (including Bahia grass, Paspalum notatum) are significant grass pollen allergen sources (1-5). Bahia grass is endemic to subtropical regions of America. It was introduced elsewhere, including Australia, for agricultural purposes (6). Compared to temperate grass species such as Timothy grass and Perennial Ryegrass, which pollinate during spring and early summer, the pollination period of Bahia grass extends from spring through autumn, therefore triggering allergic rhinitis and asthma late in the grass pollen season (2,7).
Bahia grass is widely used for animal forage and for erosion control (8). In some countries, it is used for the establishment of lawns (8). It invades disturbed pastures, roadsides, and rights-of-way easily, but does not appear to invade intact, undisturbed, native systems.
Bahia grass pollen contains many proteins (9), but only four (with estimated molecular weights of 28, 31, 33 and 60 kDa) appear to have allergenic reactivity (9,10). A protein of approximately 27-29 kDa was reported to be a major allergen (now known as Pas n 1), being reactive with serum IgE from each of 12 grass pollen-allergic patients evaluated, and a 60 kDa protein was IgE reactive with sera from four of the patients (11). Other authors have reported a 33 kDa protein to be the most reactive (10).
The following allergen(s) have been characterised:
Pas n 1, a 29 kDa protein, a beta-expansin 1 glycoprotein, a member of the Group 1 Grass family, a major allergen (7, 11-14).
In an Australian study, 29 of 34 (85%) consecutive patients presenting with grass pollen allergy were skin-prick test positive to Bahia grass pollen. Recombinant Pas n 1 reacted with serum IgE in 47 of 55 (85%) Bahia grass pollen-allergic patients (7).
Bahia grass is in the same subfamily as Johnson grass, Maize and sorghum and belongs to the same genus as Dallis grass (P. dilatatum) (8).
Bahia grass is phylogenetically distinct from other allergenic grass species. Bahia grass is classified in the Panicoideae subfamily whereas Ryegrass, Timothy grass and other clinically important grasses belong to the Pooideae subfamily of temperate grasses (15).
Extensive cross-reactivity among the different individual species of the genus could be expected, as well as among members of the family Poaceae, to a certain degree; and cross-reactivity between Bahia grass (g17), Johnson grass (g10) and Maize pollen (g202) can be expected, as they are closely related through the subfamily Panicoideae (16,17).
In an early neutralisation study in 1971, Bahia grass was said not to share any major antigens with Bermuda, Johnson and/or Timothy grass, but did share antigens with Dallis grass, although Bahia grass also contained additional specific allergens (8). Other researchers reported that Bahia grass shared allergenicity with Timothy, Meadow, Rye-, Redtop, Meadow Fescue, and Sweet Vernal grass, but also possessed unique allergens (18). More recent studies have not been able to confirm cross-allergenicity between Bahia and Timothy grass (3,19).
Limited immunological cross-reactivity was found between Timothy grass pollen and Bahia grass pollen, based on in vivo nasal allergen challenges (3), and between Ryegrass pollen and Bahia grass pollen in serum IgE ELISA analysis (7).
In a study evaluating Ryegrass pollen-allergic patients and IgE cross-reactivity between Bahia and Ryegrass, the majority of Ryegrass-allergic patients were also serum IgE-reactive to Bahia grass pollen. However, Bahia grass and Ryegrass had only limited IgE cross-reactivity, which indicated that Bahia grass should be considered in diagnosis and treatment of patients with hay fever late in the grass pollen season. The major Ryegrass pollen allergens, Lol p 1 and Lol p 5, did not show IgE reactivity with allergens of Bahia or Bermuda grasses. Timothy, Canary and Ryegrass inhibited IgE reactivity with Ryegrass and Bahia grass, whereas Bahia, Johnson and Bermuda grass did not inhibit IgE reactivity with Ryegrass. The authors concluded that Bahia appears to be largely immunologically distinct from other clinically important allergenic grasses, and therefore should be considered in the diagnosis and treatment of patients presenting with rhinitis late in the summer (11).
Pas n 1 has sequence homology with the beta-expansin 1 glycoprotein family, 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) (7).
Pollen extracts of two trees, Callistemon citrinis (Bottlebrush) and Melaleuca leucadendron (Melaleuca), as well as the grass Paspalum notatum (Bahia) were analysed for antigenic and allergenic cross-reactivity. Clinical studies demonstrated that 81% of patients who were skin test-positive to at least one of the pollens were also positive to the other two. Sixty-three percent of allergic individuals studied showed a high correlation between skin test results and the number of IgE-binding components analysed by immunoblotting. These IgE-reactive components were detected in the molecular weight range of 29 to 66 kDa. Each patient's serum had a unique IgE-binding pattern, indicating heterogeneity of immune response; however, common major determinants were detected by a large percentage of the allergic patients’ sera (9).
Bahia grass is a significant aeroallergen, which can induce asthma, allergic rhinitis and allergic conjunctivitis (1-5, 8). Compared to temperate grass species such as Timothy grass and Perennial Ryegrass, which pollinate during spring and early summer, the pollination period of Bahia grass extends from spring through autumn, therefore triggering allergic rhinitis and asthma late in the grass pollen season (2,7). Bahia grass should be considered in diagnosis and treatment of patients with hay fever late in the grass pollen season. As Bahia grass appears to be mostly immunologically distinct from other clinically important allergenic grasses, it should be considered in the diagnosis and treatment of patients presenting with rhinitis late in the summer (11).
In a study of 38 subjects in Florida, USA, who were challenged (25 nasal, 13 bronchial) with Bahia grass pollen extract, a positive Bahia intradermal skin test predicted a positive challenge to Bahia in all (11 of 11) of the nasal challenges and 75% (6 of 8) of the bronchial challenges. Specific IgE antibodies to Bahia pollen were detected (greater than or equal to 2+) in 82% (14 of 17) of subjects with positive challenges, and in 5% (1 out of 20) of subjects with negative challenges (3).
In an Australian study evaluating recombinant Bahia grass allergen Pas n 1, 29 of 34 (85%) consecutive patients presenting with grass pollen allergy were skin-prick test positive to Bahia grass pollen. All reported seasonal rhinitis and six seasonal asthma, and serum IgE varied from 0.51 kU/l to 38.5 kU/l. All were also sensitised to Rye grass and Bermuda grass pollen. Recombinant Pas n 1 reacted with serum IgE in 47 of 55 (85%) Bahia grass pollen-allergic patients (7).
In a 1971 study of 429 patients living in Louisiana, USA, aged from 5 months to 84 years, all with respiratory allergy (except 28 patients who had one of atopic dermatitis, urticaria and/or insect allergy), 51 were skin-prick positive to Bermuda grass, Johnson grass and Timothy, but not to Bahia grass. Two hundred and forty-six patients were sensitive to Bahia grass. Fourteen were sensitive only to Bahia grass. One hundred and twelve patients were sensitive to Bermuda but not to Bahia grass, 115 were sensitive to Johnson grass and not to Bahia grass; and of 93 with positive skin reactions to Timothy were negative to Bahia grass. Five volunteers all showed reactions to Bahia grass as well as Dallis grass on the first challenge (8).
Various studies around the world have demonstrated the importance of Bahia grass as an aeroallergen. A study conducted in New South Wales, Australia, demonstrated an association between Bahia grass and asthma in children (2). In Cartagena, Colombia, 28% of 99 subjects with acute asthma were found to be sensitised to Bahia grass (20). In 100 Thai patients with allergic rhinitis, 16% were positive to Bahia grass pollen in skin tests (21).
Aerobiological and clinical studies in Kuala Lumpur, Malaysia, have documented the importance of Bahia grass pollen in the exacerbation of asthma and allergic rhinitis. Of the 29.5% asthmatics with positive skin-prick test reactions, 21.5% (43 of 200) were positive to one or more of the grass pollens, of which 6.5% were positive to Bahia grass (22).
Compiled by Dr Harris Steinman, developer of Allergy Advisor, http://allergyadvisor.com
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