Oilseed rape pollen allergenicity
The cruciferae family (including the genus Brassica) are highly allergenic and this is supported by a considerable number of reports and studies in the literature. Sensitisation and allergic manifestations due to respiratory contact, skin contact and ingestion of foods containing brassica derivatives are very common. Due to the high allergenicity of cruciferae family, cross-reactivity within this plant family is common. Again this is well supported in the literature. Recently this position was reinforced by the paper presented by Poikonen in 2006 titled ‘Turnip rape and oilseed rape are new potential food allergens in children with atopic dermatitis’. Poikonen concludes; turnip rape and oilseed rape are potentially important allergens in infants and young children.
The allergenicity of oilseed rape pollen has been a matter of considerable debate amongst scientists studying oilseed rape allergy over the last two decades. This problem was highlighted and clearly defined in Hemmer’s 1997 paper titled ‘Oilseed rape pollen is a potentially relevant allergen’. Hemmer concluded; the results [of his study] suggest that oilseed rape pollen is a moderate but true source of allergy and may sensitise despite low pollen exposure.
The scientific debate was caused by the lack of consistency and variability of allergenicity of pollen extracts used during previous research projects to determine sensitisation of exposed patients using RAST and skin prick tests. This does not suggest (as some have intimated) that oilseed rape pollen has a low propensity to cause sensitisation, it merely confirms that the scientific methods used to determine sensitisation in previous studies was faulty which meant that making comparisons between studies was extremely difficult and interpretation of the results almost impossible.
A possible link (cross-reactivity) with grass pollen had been suggested as a possible causal factor in 1997 (IEH Assessment A3). However, this was subsequently rejected by Welch in 2000 who advised that: Despite allergens of similar molecular weights being present in both [oilseed rape and grass] pollen types, which may suggest common allergens, inhibition immunoblot studies confirmed that the allergens in the two pollens were immunologically distinct. Grass pollen was unable to inhibit the binding of IgE to oilseed rape and similarly oilseed rape did not inhibit the binding of IgE to grass pollen, although there was complete self-inhibition. Thus there was no evidence of any cross-reactivity with grass pollen.
The conclusions by Welch are hardly surprising. Allergists have understood and studied cross-reactivity for many years. Cross-reactivity within plant families is common (e.g. cruciferae), however, the author is not aware of any instances of cross-reactivity outwith plant families. Although this may well change at some point in the future with the development of GM crops.
Occupational sensitisation to oilseed rape pollen was demonstrated by Fell in 1992. Individuals occupationally exposed to oilseed rape are at an increased risk of developing specific IgE and associated symptoms: 35% of specialist plant breeders working closely with oilseed rape developed sensitisation.
Whilst it is true that plant breeders (exposed closely to oilseed rape pollen eight hours per working day during the flowering period) are likely to develop sensitisation to oilseed rape pollen. It is also true that the public living within close proximity to rape fields (exposed to oilseed rape pollen 24/7 during the flowering period) are also likely to develop sensitisation to oilseed rape pollen. The author would hypothesise that the considerably extended period of exposure by the public living in close proximity to rape fields must present an elevated level of risk of sensitisation, albeit that pollen dispersal levels during the hours of darkness drop off considerably in comparison to dispersal during daylight hours.
Oilseed rape pollen and VOCs
The author is surprised to read from the literature that there is no evidence to confirm that the scientists have taken a holistic approach when investigating oilseed rape pollen dispersal and allergenicity. It is feasible that oilseed rape pollen could also contain traces of the naturally emitted volatile organic compounds (VOCs) from the flowering plants. Hypothetically these volatiles could either be a component of the pollen and/or become attached to the sticky outer-surface of the wind-borne pollen as it travels through the airspace laden with VOCs emitted from the crop during the flowering phase. If this hypothesis was correct, human exposure to oilseed rape pollen containing VOCs could cause immunological and/or non-immunological reactions.
This theory is supported by work carried out by Breitender & Scheiner 1990; direct contamination of pollen may occur, either on the plant or in the air. Behrendt 1992 and Bessonova 1992 reported that particles may adhere to the surface of pollen. According to IEH Assessment A3 1997, this indicated that various interactions may take place that are significant in altering the allergenicity of pollen.
Oilseed rape pollen and bronchial symptoms
Oilseed rape pollen grains are quite large (PM25) and have a sticky outer-coating. Regardless of airborne pollen dispersal and concentrations, these characteristics do not lend themselves to penetrating deep into the bronchial airways. Generally speaking, pollen grains, fungal spores and pollutants measuring PM10 or less are the ones responsible for immunological and/or non-immunological bronchial symptoms. Particles above PM10 size tend to get trapped in the nasal passage and may well be the cause of localised immunological and/or non-immunological symptoms like rhinitis, but not bronchial symptoms.
Author - Armitage; copyright 2007