Allergen of the Month—Privet

Allergen of the MonthdPrivet The genus Ligustrum contains about thirty-five species of deciduous or evergreen shrubs native to Europe, northern Africa, Asia, and Australia.1,2 Common privet, L. vulgare, is widely distributed though almost all of Europe.3 Of a dozen species introduced into North America, L. vulgare has the largest range: Nova Scotia to Ontario, British Columbia, and across most of the United States. Privets were introduced as ornamentals and hedges, with L. vulgare first brought in the 1700s.2 Privets grow along woodland edges, in floodplains, and riparian forests. The fruits are poisonous but give a black dye previously used by hatters and glove-makers, and to color wine; and the branches have been used in basket-making.3 Common privet is a deciduous or semi-evergreen shrub with height and spread of 3 m. Leaves are lance-shaped and dark green. Clusters of white tubular flowers have four petals and two protruding anthers.4 Pollination in Europe and northeastern United States occurs May through June, while earlier in the southern states and later in the southwest.3e5 Despite being primarily insect-pollinated, privets are facultatively anemophilous and pollen can be easily captured on samplers.6,7 Sensitization can easily be demonstrated, and skin test positivity to olive in an olive and ash-free area has been attributed to privet.6,8 Rhinitis from privet is reported, and late asthmatic responses to privet have been described.6,9 Privet is in family Oleaceae, subfamily Oleoideae, within the monophyletic order Lamiales. Because of some divergence from other families in Lamiales, Oleaceae is sometimes placed in a separate order, Oleales.10 Cross-reactivity assessed by RAST inhibition is strong between Oleaceae members: privet, olive (Olea), ash (Fraxinus), Forsythia, and Phillyrea.11,12 At least eleven olive allergens have been characterized: the most important being the shared group 1 allergen, Ole e 1; panallergens such as profilin and calmodulin have been identified as well.13 The major privet allergen, Lig v 1, has been characterized and cloned.14 L. vulgare grains are oblate 28.5 mm in diameter, tricolporate. Furrows are sharply defined, 17.3x5.0 mm, with smooth membrane. Well-defined pores are circular to slightly elliptical, 5.0 mm in diameter. The exine is 2.1 mm thick, with sexine 1.6 mm, and the thinner nexine about 0.4 mm. The intine is thin, swelling beneath the furrows to make shallow onci 13.0x1.8 mm thick. Sculpturing is reticulate, with the meshes varying from fine to coarse, with ridges formed of buttressed rods 1.7 mm in height, giving a beaded appearance.15,16 Text and Photography: Richard W. Weber, M.D. References [1] Wodehouse RP. Hayfever Plants, 2nd Ed. New York: Hafner Press, 1971: 141e145. [2] Kaufman SR, Kaufman W. Invasive Plants. Mechanicsburg, PA: Stackpole Books; 2007:86e88. [3] Polunin O. Flowers of Europe: A Field Guide. London: Oxford University Press; 1969:310e313. [4] Horak F, Jäger S. Die Erreger des Heufiebers. München:Urban & Schwarzenberg. 1979;39:115e116. [5] Lewis WH, Vinay P, Zenger VE. Airborne and Allergenic Pollen of North America. Baltimore: John Hopkins Press; 1983:73e79. [6] Lewis WH, Vinay P. North American pollinosis due to insect-pollinated plants. Ann Allergy. 1979;42:309e318. [7] Cariñanos P, Alcázar P, Galán C, Dominguez E. Privet pollen (Ligustrum sp.) as potential cause of pollinosis in the city of Cordoba, south-west Spain. Allergy. 2002;57:92e97.

[8] Asero R. Analysis of hypersensitivity to oleaceae pollen in an olive-free and ash-free area by commercial pollen extracts and recombinant allergens. Eur Ann Allergy Clin Immunol. 2011;43:77e80. [9] Richards G, Kolbe J, Fenwick J, Rea H. The effects of privet exposure on asthma morbidity. N Z Med J. 1995;108:96e99. [10] Judd WS, Campbell CS, Kellogg EA, Stevens PF. Plant Systematics: A Phylogenetic Approach. Sunderland, MA: Sinauer Associates; 1999: 369e373. [11] Bousquet J, Guerin B, Hewitt B, et al. Allergy in the Mediterranean area. III. Cross reactivity among Oleaceae pollens. Clin Allergy. 1985;15:439e448. [12] Weber RW. Cross-reactivity of plant and animal allergens. Clin Rev Allergy Immunol. 2001;21:153e202. [13] Weber RW. Cross-reactivity of pollen allergens: impact on allergen immunotherapy. Ann Allergy Asthma Immunol. 2007;99:203e212. [14] Batanero E, Gonzalez De La Peña MA, Villalba M, et al. Isolation, cDNA cloning and expression of Lig v 1, the major allergen from privet pollen. Clin Exp Allerg. 1996;26:1401e1410. [15] Hyde HA, Adams KF. An Atlas of Airborne Pollen Grains. London: MacMillan & Co; 1958:63. [16] Erdtman G. An Introduction to Pollen Analysis. Waltham, MA: Chronica Botanica Co; 1954:114.

Reprints: Richard W. Weber, M.D. National Jewish Health 1400 Jackson Street Room J326 Denver, CO 80206