Velvet grass

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Code: g13
Latin name: Holcus lanatus
Source material: Pollen
Family: Poaceae (Gramineae)
Sub family: Pooideae
Tribe: Aveneae
Common names: Velvet grass, Yorkshire Fog
A grass species producing pollen, which often induces hayfever, asthma and conjunctivitis in sensitised individuals.

Allergen Exposure

Geographical distribution
Velvet grass is native and common to most of Europe, though it is absent in the northernmost regions. It now has a worldwide distribution including temperate regions in western Eurasia, the USSR, and Australia. It was introduced in North America, where it is occasionally cultivated as meadow. The name Velvet grass perhaps comes from the appearance its pale purple flower heads make when growing amassed in an open field. In many countries H. lanatus is considered a weed and only of minor importance for grazing.
 
This perennial bunchgrass may, on the other hand, be named for the soft, whitish hairs (of two distinct lengths) on the stem, leaves and even inflorescence branches. The leaves, mostly basal and with distinct-textured leaf sheaths that can have a purplish colour, are up to 20 cm long and 10 mm wide; the stem and flower spikes provide additional height, typically up to 60cm but occasionally higher.
 
The inflorescences are silvery to green to purplish, paniculate, erect or nodding, open or contracted, often oblong or ovate, sometimes almost spike-like, 8 to 15 cm long, and occasionally enclosed within the uppermost sheath. The spikelets number 2 to 3 on a typical ultimate inflorescence branch. There are typically 2 to 3 white hermaphrodite florets per 4- to 4.5 mm-long spikelet. There are occasional rudimentary or incomplete florets (male, without ovarian structure). Velvet grass flowers in late summer. The propagation is via seed, which is dispersed by wind. As with most bunchgrasses, this species tolerates fires and regenerates rapidly from basal shoots.
 
Environment
It invades moist disturbed sites rapidly, overwhelming native species and forming dense stands in upland pastures, open woods, fields and grasslands, and along roadsides.
 
The flowers can be used in both fresh and dried arrangements.
 
Allergens
  • Hol l 1, a 34 kDa protein (1)
  • Hol l 5, a 30 kDa protein, a major allergen (1, 2) 
Only single isoforms have been found to Hol l 1 (3).

The major Group I allergen of Velvet grass bears at least four different IgE-binding epitopes, which were individually recognized by sera from different patients (4).
 
A Group 4 grass allergen homologue to Phl 4 (Timothy grass) was also detected in this grass pollen (5).
 
Two isoforms of Hol l 5 have been detected and designated rHol l 5.01 and rHol l 5.02. A high similarity exists between them (78% identity) and to Group 5 allergens and their isoforms found in other grass species (6).
 
Appreciable trypsin inhibitory activity has been detected in Parietaria, Olea, Ambrosia, Rumex, Chenopodium, Holcus and Poa spp. These proteins of the serpin family of anti-proteinases were found to bind specific IgE antibodies from the serum of patients with allergic rhinitis (7).

Potential Cross-Reactivity

An extensive cross-reactivity among the different individual species of the genus could be expected, as well as to a certain degree among members of the family Poaceae, especially in the subfamily Pooideae (Rye grass (g5), Canary grass (g71), Meadow grass (g8), Timothy (g6), Cocksfoot (g3), Meadow Fescue (g4), Velvet grass (g13), Redtop (g9), Meadow Foxtail (g16), Wild Rye grass (g70))
(8, 9).   
 
Velvet grass contains Group 1 allergens, to which more than 95% of patients allergic to grass pollen possess IgE antibodies. These are highly cross-reactive glycoproteins exclusively expressed in the pollen of many grasses (10, 11, 12). Group 1 allergens are highly homologous, but not all of the antigenic epitopes are crossreactive(13). Highly homologous Group 1 allergens have been demonstrated between Pha a 1 from Canary grass, 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%) (14). 
 
Velvet grass also contains a Group 4 allergen. Group 4 grass pollen allergens are glycoproteins with a molecular weight of 50 to 60 kDa, which are present in many grass species. Almost 75% of patients allergic to grass pollen display IgE reactivity to Group 4 allergens, which hence can be regarded as major grass pollen allergens(15). Inhibition studies of IgE antibody binding to Dac g 4 (Dactylis glomerata - Cocksfoot grass) with other pollen extracts confirmed the presence of cross-reactive allergens in Secale cereale (Cultivated Rye), Lolium perenne (Rye grass), Festuca elatior (Meadow Fescue), Holcus lanatus (Velvet grass), Bromus arvensis (Field Brome), Poa pratense (Meadow grass), Hordeum sativum (Barley), and Phleum pratense (Timothy grass) (16). Further, Phl p 4 homologes with similar molecular weights were detected in Dactylis glomerata (Cocksfoot grass), Festuca pratensis (Meadow Fescue), Holcus lanatus (Velvet grass), Poa pratensis (Meadow grass), and Lolium perenne (Rye grass). Group 4 homologes are present in the various grass extracts, but to different extents (17).
 
Velvet grass pollen also contains a Group 5 allergen. Almost 90% of grass pollen-allergic patients are sensitised against Group 5 grass pollen allergens. Many other grasses have been shown to contain group 5 allergens (14, 18).

Clinical Experience

IgE mediated reactions
Velvet grass pollen can induce asthma, allergic rhinitis and allergic conjunctivitis(19).
 
In 184 Costa Rican allergic rhinitis patients tested for sensitivity to Poaceae species, the highest numbers of positive specific IgE tests were for Anthoxatum odoratum (83.2%), Panicum maximum (82.1%), Panicum mole (78.3%), and Holcus lanatus (77.7%) (19).

Compiled by Dr Harris Steinman, harris@zingsolutions.com

References

  1. Schramm G, Petersen A, Bufe A, Schlaak M, Becker WM. Identification and characterization of the major allergens of velvet grass (Holcus lanatus), Hol l 1 and Hol l 5. Int Arch Allergy Immunol 1996;110(4):354-63 
  2. Schramm G, Bufe A, Petersen A, Haas H, Merget R, Schlaak M, Becker WM. Discontinuous IgE-binding epitopes contain multiple continuous epitope regions: results of an epitope mapping on recombinant Hol l 5, a major allergen from velvet grass pollen. Clin Exp Allergy 2001;31(2):331-41 
  3. Petersen A, Grobe K, Lindner B, Schlaak M, Becker WM. Comparison of natural and recombinant isoforms of grass pollen allergens. Electrophoresis 1997;18(5):819-25 
  4. Schramm G, Bufe A, Petersen A, Haas H, Schlaak M, Becker WM. Mapping of IgE-binding epitopes on the recombinant major group I allergen of velvet grass pollen, rHol l 1. J Allergy Clin Immunol 1997;99(6 Pt 1):781-7 
  5. Fahlbusch B, Muller WD, Rudeschko O, Jager L, Cromwell O, Fiebig H. Detection and quantification of group 4 allergens in grass pollen extracts using monoclonal antibodies. Clin Exp Allergy 1998;28(7):799-807 
  6. Schramm G, Bufe A, Petersen A, Schlaak M, Becker WM. Molecular and immunological characterization of group V allergen isoforms from velvet grass pollen (Holcus lanatus). Eur J Biochem 1998;252(2):200-6 
  7. Berrens L, Maranon F. IgE-binding trypsin inhibitors in plant pollen extracts. Experientia 1995;51(9-10):953-5 
  8. Yman L. Botanical relations and immunological cross-reactions in pollen allergy. 2nd ed. Pharmacia Diagnostics AB. Uppsala. Sweden. 1982: ISBN 91-970475-09 
  9. Yman L. Pharmacia: Allergenic Plants. Systematics of common and rare allergens. Version 1.0. CD-ROM. Uppsala, Sweden: Pharmacia Diagnostics, 2000. 
  10. Grobe K, Becker WM, Schlaak M, Petersen A. Grass group I allergens (beta-expansins) are novel, papain-related proteinases. Eur J Biochem 1999;263(1):33-40 
  11. Schenk S, Breiteneder H, Susani M, Najafian N, Laffer S, Duchene M, Valenta R, Fischer G, Scheiner O, Kraft D, Ebner C. T cell epitopes of Phl p 1, major pollen allergen of timothy grass (Phleum pratense). Crossreactivity with group I allergens of different grasses. Adv Exp Med Biol 1996;409:141-6 
  12. Hiller KM, Esch RE, Klapper DG. Mapping of an allergenically important determinant of grass group I allergens. J Allergy Clin Immunol 1997;100(3):335-40 
  13. Esch RE, Klapper DG. Cross-reactive and unique Group I antigenic determinants defined by monoclonal antibodies. J Allergy Clin Immunol 1987;78:489-95 
  14. Suphioglu C, Singh MB. Cloning, sequencing and expression in Escherichia coli of Pha a 1 and four isoforms of Pha a 5, the major allergens of canary grass pollen. Clin Exp Allergy 1995;25(9):853-65 
  15. Fischer S, Grote M, Fahlbusch B, Muller WD, Kraft D, Valenta R. Characterization of Phl p 4, a major timothy grass (Phleum pratense) pollen allergen. J Allergy Clin Immunol 1996;98(1):189-98 
  16. Leduc-Brodard V, Inacio F, Jaquinod M, Forest E, David B, Peltre G. Characterization of Dac g 4, a major basic allergen from Dactylis glomerata pollen. J Allergy Clin Immunol 1996;98(6 Pt 1):1065-72 
  17. Fahlbusch B, Muller WD, Rudeschko O, Jager L, Cromwell O, Fiebig H. Detection and quantification of group 4 allergens in grass pollen extracts using monoclonal antibodies. Clin Exp Allergy 1998;28(7):799-807 
  18. Klysner S, Welinder KG, Lowenstein H, Matthiesen F. Group V allergens in grass pollens: IV. Similarities in amino acid compositions and NH2-terminal sequences of the group V allergens from Lolium perenne, Poa pratensis and Dactylis glomerata. Clin Exp Allergy 1992;22(4):491-7 
  19. Riggioni O, Montiel M, Fonseca J, Jaramillo O, Carvajal E, Rosencwaig P, Colmenares A. Type I hypersensitivity to gramineae pollen (by species) in allergic rhinitis patients. [Spanish] Rev Biol Trop 1994;42 Suppl 1:71-6, 20

As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.