Environmental and Food Allergens

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Environmental and Food Allergens

• Carla Davis, MD
• Research Fellow
• Division of Allergy and Immunology
• Department of Pediatrics
• Texas Childrens Hospital
• Baylor College of Medicine

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Outline

• Definition of aeroallergen
• Collection Devices
• Pollen Identification
• Fungal Identification
• Indoor Allergens
• Food Allergens
• Clinical consequences of cross reactions

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Definition

• Aeroallergens are airborne particles that induce
  allergic reactions in sensitized subjects and can
  cause respiratory, cutaneous, or conjunctival
  allergy
• They can range from submicronic particles to
  relatively larger pollen grains, fungal spores
  and animal emanations
• To be clinically significant, they must be
  buoyant, present in significant concentration and
  allergenic

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Sampling Devices

• For airborne allergens, several methods exist to
  quantify pollen grains and fungal spores
• The devices rely on microscopic observation with
  counting of particles captured on collecting
  surfaces
• Site selection is important and should be chosen
  for the specific situation (urban, rural or
  indoor conditions)

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Sedimentation/gravity sampler

• Standard device is a Durham sampler
• A microscopic slide coated with petroleum jelly
  or silicone grease placed adhesive side up
  between a pair of parallel circular plates 3
  inches apart (agar plate also used)
• After exposure, slides are stained with
  Calberlas solution (utilizes basic fuchsin), the
  pollen or fungi are identified and counted

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Durham sampler

• Advantages
• Low cost
• Spores are culturable
• Disadvantages
• Not quantitative
• Collects particles well if gt10 µm
• No separation of sizes of allergens

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Rotating arm impactor samplers

• Standard device is a Rotorod sampler
• Plastic rods are mechanically rotated to increase
  the trapping efficiency of the narrow collection
  surface
• The adhesive rod assembly is rotated at about
  2000 rpm to stimulate increased wind velocity
• Volume sampled is calculated

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Rotorod sampler

• Advantages
• Volumetric sampling
• Simple operation
• Moderate cost
• Disadvantages
• Not efficient for small particles (lt10 µm)
• Spores are not culturable
• Sizes are not separated

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Suction device (wind directed)

• Standard device is a Burkard sampler
• A lightweight cylindrical device operating at 10
  L/min with a 14 x 2 mm slit in the top
• The particles impact onto an adhesive coated
  microscope slide inserted through the side of the
  unit
• Another type is called Allergenco MK-3

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Burkard sampler

• Advantages
• Volumetric sampling
• Collects small particles well (gt 5 µm)
• Good for personal sampling
• Disadvantages
• High cost
• No separation of sizes
• Spores nonculturable

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Cascade impactors

• Standard device is an Anderson sampler
• It collects particles directly on culture media
  positioned at 1,2 or 6 stages with each plate
  representing viable particles of a different size
  fraction
• Particles of 1 µm or less are studied

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Anderson sampler

• Advantages
• Volumetric detection
• Small sizes detected well
• Spores are culturable
• Sizes are separated
• Disadvantages
• High cost
• Must be manually positioned toward the airflow in
  moving air so usually restricted to indoor
  sampling

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Pollen identification

• Pollen dispersion is by wind (anemophilous), by
  insect (entomophilous) or by both (amphiphilous)
• Outer wall of pollen grain is the exine
• Exine is composed of inner nexine and outer
  sexine
• Inner wall of pollen grain is the intine
• Grains with circular or elliptical openings are
  porate
• If the pore has a cap or plug, this is the
  operculum
• Thickening of the exine around a pore is an aspis
  and ring around a pore is an annulus

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Pollen identification

• Slits or boat shaped areas of the thin exine are
  called furrows and grains with furrows are
  colpate
• Pollens with both furrows and pores are colporate
• Smooth surfaced grains are psilate , grains with
  spines are echinate, and grains with rods are
  baculate

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Pollen Identification

• Pine is inaperturate (no pores or furrows) with
  two air bladders, sized 40-100 µm
• Think Mickey Mouse cap
• Cedar and cottonwood are inaperturate and psilate
  (smaller than pine with size from 20-35 µm)

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Pine
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Grass Identification

• Grasses are very similar being monoporate with a
  prominent operculum
• Size ranges from 20 to 60 µm

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Salt grass
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Tricolporate grains

• Ragweed (Ambrosia) has short furrows with
  indistinct pores while Sages (Artemisia) have
  more apparent apertures
• Ragweed has short broad based spines and Sages
  are without spines

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Ragweed
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Sage
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Periporate grains

• Plaintains have between 6 and 11 pores
• Amaranth and Chenopods are also periporate with
  20 to 80 pores per grain (this includes careless
  weed, pigweed, lambs quarter, and russian
  thistle)

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Pigweed
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Triporate grains

• Birch has tri to pentaporate grains with pore
  associated finding such as annuli, aspidae, and
  arci
• Hickory and pecan are triporate with pores evenly
  spaced close to the equatorial plane

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Birch
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Tricolpate grains

• Maple
• Ash
• Chestnut
• Box Elder
• Olive, Oak
• Willow
• All have grains with three furrows

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Maple
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Oak
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Willow
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Common name Genus/Species

• Trees
• Birch Betula verrucosa (Bet v 1,2,3)
• Oak Quercus albus (Que a 1)
• Hazel Corylus avellana (Cor a 1)
• Olive Olea europaea (Ole e 1)
• Japanese cedar Cryptomeria japonica (Cry j 1)
• Mountain cedar Juniperus ashei (Jun a 1)
• Cypress Cupress arizonica (Cup a 1)
• Japanese cypress Chamaecyparis obtusa (Cha o 1)

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Common name Genus/Species

• Grasses
• Rye Lollum perenne (Lol p 1-5)
• Timothy Phleum pratense (Phl p 1-6)
• Bermuda Cynodon dactylis (Cyn d 1)
• Johnson Sorghum halepense (Sor h 1)
• Weed
• Short Ragweed Ambrosia artemisiifolia
• (Amb a 1)
• - Mugwort Artemisia vulgaris (Art v 1)

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Fungal Identification

• For fungal sampling, suction or cascade samplers
  are most efficient
• The most direct way is to measure fungal allergen
  concentration in airborne or settled dust
  samples, but there are limitations in the
  measurement by immunoassay techniques
• Currently, no standard method exists for
  collection and identification
• Indoor spore counts over 1000/m3 are thought to
  be suggestive of mold contamination

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Characterized fungal allergenic proteins

• Alternaria alternata (Alt a 1)
• Cladosporium herbabarium (Cla h 2)
• Aspergillus fumigatus (Asp f 1)
• Penicillium chrysogenum/notatum (Pen ch 13)
• Penicillium citrinum (Pen c 3)
• Candida albicans (Cand a 1)
• Trichophyton tonsurans (Tri t 1)
• Trichophyton rubrum ( Tri r 1)
• Basidiomycota Malassezia furfur (Mala f 1),
  Coprinus comatus (Cop c 1), Psilocybe cubensis
  (Psi c 1)

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Aspergillus fumigatus
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Alternaria
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Penicillium
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Cladosporium
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Indoor allergens

• Major cat allergen Felis domesticus (Fel d 1)
• Found in saliva and skin from sebaceous glands
  (primary site of production is the skin)
• Minor allergens Fel d 2 (cat albumin) and Fel d 3
  (a cystatin) only cause sensitization in a
  minority of cat allergic patients.
• Cat allergen is tenacious and can remain for
  months after a cat is removed from the home
• Vectors carrying allergen are very small (lt25 µm)
  and stay airborne for a long time

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Indoor allergens

• Major dog allergen is Canis familiaris (Can f 1)
  which is detected on the coat and in saliva
• Dust mite allergens are currently grouped into 2
  classes
• Group 1 includes Der p1 and Der f 1, cysteine
  proteases with homology to papain
• Group 2 includes Der p 2 and Der p 2, homologous
  proteins to the primate epididymus protein
• Der f 3/Der p 3 are serine proteases

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Indoor allergens

• Cockroach major allergens
• Blattella germanica and Periplaneta americana are
  the two species most known
• Studies of cockroach allergen Bla g 2 in the air
  have shown little or no allergen except during
  vacuum cleaning
• Potentially the allergen becomes airborne on
  relatively large particles which fall quickly
  after disturbance

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Indoor allergens

• Mouse (Mus musculus) major allergen is Mus m 1, a
  urinary protein whose function is pheromone
  bonding
• Rat (Rattus norvegicus) major allergen is Rat n
  1, urinary per albumin
• Both can induce IgE and IgG antibodies in animal
  handlers and scientists working with these animals

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Food allergy

• Class 1 food allergy is considered traditional
  because it denotes sensitization to food
  allergens through the gastrointestinal tract
• Water soluble glycoproteins which are stable to
  treatment with heat, acid, and proteases
• Class 2 food allergy denotes sensitization to
  food as a consequence of an allergic
  sensitization to inhalant allergens
• Plant derived proteins highly heat labile and
  difficult to extract

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Cows milk allergens

• as1-Casein (Bos d 8 - Bos domesticus)
• as2-Casein
• ß-Casein
• ?-Casein
• Whey
• ß-Lactoglobulin (Bos d 5)
• a-Lactalbumin (Bos d 4)
• Serum albumin (Bos d 6)
• Studies have suggested recently that casein
  proteins are the more allergenic

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Egg allergen

• Chicken Egg White
• Accounts for the most common IgE mediated food
  allergy in children
• Yolk less allergenic than the white
• Ovalbumin ( Gal d 1 )
• Ovomucoid ( Gal d 2 ) responsible for the vast
  majority of clinical reactivity in egg allergic
  children
• Ovotransferrin ( Gal d 3 )
• About half of children allergic to eggs can
  ingest small amounts of egg protein in
  extensively heated (baked) products (lack IgE to
  sequential vs. conformational epitopes)

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Peanut/Soybean Allergens

• Peanut most common food allergy above age 4
  years
• Vicilin family of seed storage proteins- Ara h 1
  
• Conglutin family of storage proteins- Ara h 2
• Glycinin family of seed storage proteins - Ara h
  3
• Soybean
• Glycinin G1 acidic chain allergenic epitopes
  are homologous to Ara h 3
• Profilin is an actin bonding protein first
  identified in Birch pollen (Bet v 2) and is seen
  in Gly m 3 as well as a number of other fruits
  and vegetables

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Seafood Allergens

• Fish
• The major allergen in codfish is Parvalbumin- Gad
  c 1 (Gadus callarias)
• Shrimp
• The major allergen in shrimp is Tropomyosin - Pen
  a 1 (Penaeus species)
• Invertebrate tropomysins are highly homologous
  and tend to be allergenic (those from
  crustaceans, dust mites, cockroaches and
  mollusks)

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Lipid Transfer Proteins

• Lipid Transfer Protein Allergens
  (pathogen-related proteins group 14)
• Apple - Mal d 3
• Apricot - Pru ar 3
• Peach - Pru p 3
• Plum - Pru d 1
• Corn - Zea m 14
• When fruit allergy develops in the absence of
  pollen allergy, there is evidence to suggest
  reactions are directed at LTPs

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Class 2 Food Allergens (Cross-reactive and
Associated with Oral Allergy Syndrome)

• Pathogen-related protein 5
• Apple Mal d 2 Thaumatin-homologue
• Cherry Pru av 2 Thaumatin
• Birch Bet v 1 Homologues (pathogen-related
  protein 10)
• Apple Mal d 1
• Cherry Pru av 1
• Apricot Pru ar 1
• Pear Pyr c 1
• Carrot Dau c 1
• Celery Api g 1
• Parsley pcPR 1 and 2
• Hazelnut Cor a 1

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Homologous pathogen related protein

• Birch Bet v 2 Homologues (celery-mugwort-spice
  syndrome)
• Latex Hev b 8
• Celery Api g 4
• Potato
• Cherry Pru av 4
• Pear Pyr c 4
• Peanut Ara h 5
• Soybean Gly m 3

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Pollen Food Syndrome Association
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Conclusions

• As allergists/immunologists it is important for
  us to be able to identify the allergen/antigens
  that are causing our patients symptoms
• Homologous proteins in cross reacting foods may
  cause serious clinical consequences