First aerobiological study in Mediterranean part of Croatia (Dalmatia): pollen spectrum and seasonal dynamics in the air of Split

The aim of this study was to investigate aerobiological dynamics of pollen in the Mediterranean part of Croatia in the air of the city of Split. Pollen monitoring during the period from 2005 to 2013 was performed using a Hirst volumetric trap. Among the identified pollen of 50 taxa, 21 were allergenic. The average annual pollen index was 33,513. Three pollination seasons were established: early winter season dominated by tree pollen, spring–summer season dominated by herbaceous plants and summer–autumn season with lower amounts of Parietaria and Cupressaceae pollen. According to the abundance, the main taxa were: Cupressaceae, Parietaria/Urtica, Pinus, Quercus, Olea, Carpinus/Ostrya, Poaceae, Platanus and Ambrosia. The annual pollen index together with the daily maximum concentrations showed an upward trend for selected taxa during the study period. The highest monthly pollen index and the highest biodiversity were recorded in April and the lowest during the late autumn and winter months. The pollen calendar created for the city of Split confirmed Mediterranean features of the pollen spectrum. The longest pollen seasons were recorded for Cupressaceae, Parietaria/Urtica and Poaceae pollen types. The correlations between pollen concentrations and meteorological parameters were analyzed. The correlations between pollen concentrations and temperature were positive, while the humidity and the precipitation mostly showed negative influence.     

Parietaria pollen a new aeroallergen in the city of Valparaiso, Chile

Parietaria pollen has never been considered as a significant cause of pollinosis in Chile; therefore, the sensitization to Parietaria study has never been included in the study of patients with clinical suspicion of pollinosis in this region. The objective of this study was to describe the clinical characteristics of pollinosis caused by Parietaria in the Valparaíso region, related to air concentrations of this kind of pollen. A cross-sectional study was performed in the city of Valparaíso. It consisted of two stages: In the first, pollen grains were counted between 1999 and 2001. In the second, a sensitization profile on a patient population diagnosed with ARC (allergic rhinoconjunctivitis) was evaluated. Parietaria judaica (P. judiaca) presented pollination all year long, with aggravation in the spring and summer, and with values reaching 80 grains/m³ (weekly average). These findings determined the transience of the symptoms in this population, which is mainly perennial with seasonal aggravations. A total of 72 atopic subjects were obtained during the whole sample recollection period. P. judaica was the second most frequent cause of sensitization (60 %) after Dermatophagoides in the sample overall. Also, in monosensitized subjects, it was the first cause of pollen sensitization. P. judaica represents the second cause of allergy in Valparaíso and the first cause of pollinosis. These findings suggest the importance of quantifying Parietaria in Valparaíso and near cities, plus investigating the presence of sensitization and symptoms to allergies in a significant proportion of patients in this region.     

Computer-aided identification of allergenic species of Urticaceae pollen

Plant species of the family Urticaceae have periods of extensive and overlapping flowering. Two genera Urtica (U. urens L., U. membranacea Poir. in Lam) and Parietaria (P. judaica L.) are abundant throughout the Iberian Peninsula. Both have substantial allergenic potential, but patient sensitivity is specific to each genus. As a result, interest from the medical profession in the identification of the pollen from these genera has arisen. It would be useful to be able to estimate the relative percentages of pollen of these genera in the air, which would allow clinicians to recommend the appropriate safety measures to patients. Unfortunately, palynologists are unable to distinguish between the species of genera (Parietaria and Urtica). Additionally, traditional methods of pollen counting are laborious and therefore not optimal for routine on-line analysis. Recent biometrical analysis enables us to discriminate between pollen species of the genera Parietaria and Urtica, but they fail to solve the problem of genera identification. Alternative methods for counting and distinguishing genera of Urticaceae have long been awaited by medical experts among others. In this paper we present a computational system to discriminate between genera by using image analysis. It is based on the definition and computation of digital shape measures on pollen images taken by an optical microscope. The system correctly classifies more than 86% of all experiments done. A set of shape parameters are tested and the subset with the highest discrimination power includes: area (A), diameter (DM), mean distance to centroide (D_mean) and roundness (R) of the pollen grain.     

Pollinosis in trentino (Northern Italy). Aerobiological and clinical research

Summary A study to evaluate and define the atmospheric pollen concentration in Trentino was carried out through the aerobiologic sampling in three localities chosen according to their different climatic conditions.1375 patients with pollinosis living in Trentino were studied retrospectively over the period ranging from 1986 to 1988 and selected according to the area they came from.Results have proved that the most allergenic pollen types are the following: Poaceae, Urticaceae (Parietaria), Compositae (Artemisia) and the tree pollen of Betulaceae and Corylaceae (Alnus, Betula, Corylus), and that pollinosis caused by such pollen, types has different features and frequencies according to the different localities.As far as symptoms are concerned, our data shows that rhinoconjuntivitis is more frequent in those patients who are allergic toParietaria while asthma results being more frequent in patients who are allergic to tree pollen.     

Gramineae hay fever,and aerobiological and clinical investigation in Palermo; Sicily

Summary Epidemiological and aerobiological observations (1987;1989) have been carried out for three years in order to search the existing relationship between the Gramineae's daily pollen concentration in Palermo's atmosphere and the number of hay fever cases due to such pollen.The aerobiological data were obtained with a 2000 VPPS volumetric sampler. Clinical research was performed on 555 hay fever patients treated in our ambulatory over a three-year period (1987–1989).These data, elaborated by a seven day running mean method and correlated with epidemiological data, evidenced that three of the pollen families in our territory are clinically important: Urticaceae,Parietaria prevailing among them, Gramineae and Oleaceae,Olea europaea prevailing among them.The Gramineae are the second most important allergenic pollen (32,08% of all the pollinosis) whereas, as far as its concentration in the atmosphere is concerned; it ranks third followingParietaria and Oleaceae.     

Histochemical properties and trace element concentrations in <Emphasis Type="Italic">Parietaria L.</Emphasis>from urban sites (Palermo,Italy)

We examined leaf and pollen histochemical properties in Parietaria L. and measured trace element concentrations in urban sites in Palermo, Sicily, affected by different stress valence levels. Urban pollution affects histochemistry macro-, micro-, and toxic element concentrations in Parietaria. We therefore decided to determine whether this plant can be used as a simple biomonitor or bioaccumulator of pollution contaminants. Samples were collected at various sites in different periods. An increase in phenolic compound levels was a result of the impact of pollution. Histochemical characteristics and trace element concentrations varied according to the period, but not to the place, of sampling. Pollutant concentrations were the highest in the month of February 2002. Trace metal concentrations were the lowest in July. Our investigations have confirmed that Parietaria L. can be used to study the effects of trace elements in the atmosphere in urban sites; in fact, they are veritable accumulators, given that elevated levels of pollutants can be found on their structures with no visible morphological effects. There are differences in accumulation capacity according to the trace elements studied. Pollution alters the content of phenolic compounds and chemical elements in Parietaria L.     

Trend of herbaceous pollen diffusion and allergic sensitisation in Genoa, Italy

In order to investigate the relationship betweenallergenic load and allergic sensitisation prevalenceon a long period, we analysed the annual data ofherbaceous pollen airborne diffusion in Genoa(NW-Italy) for 17 years (1981–1997), with particularregard to the most important allergenic species:Poaceae, Parietaria, Artemisia, Ambrosia. Weevaluated the relative trend and compared it with theprevalence data of patients sensitisation to thesepollens in the same period.The analysis of annual pollen amount revealed asignificant rising trend (r = 0.73, p < 0.05) of Parietaria pollen (average 14.324 grains/m³/year),whereas Poaceae (2048/year) and Artemisia(170/year) pollen count did not show any significantchange. Ambrosia (average 70/year) has been rising since 1989 (r = 0.87, p < 0.05) and reached themaximum pollen count in the last three years.The prevalence of pollen sensitisation resulted to bevery high (about 75%) in our atopic patients withrespiratory symptoms and did not change significantlyin the years: Parietaria pollen allergy waspresent in about 70% of patients with at least oneSPT positive to pollens (and 55% of atopicsubjects), and this frequency, much higher than theone found in North Italy, showed low year-to-year variability.Among pollinotics patients, Poaceae cutaneoussensitisation was found at a quite stable rate in theabove mentioned period (about 51%), as well as thatto Artemisia pollen (8%). Ambrosia skinprick test positivity is very rare (about 0.5%),without any evident increase.The present study shows that, for some of theherbaceous species, we cannot demonstrate astraightforward relationship between the trend ofairborne pollen and the frequency of sensitisation inexposed people. However, in the case of Parietaria, the high level of pollen amount in theair is clearly related with the high rate of cutaneous positivity in patients, but it seems tosuggest a ``plateau' that is not modified by anyfurther increase in airborne pollen (perhaps forgenetic limiting factors). On the other hand, Ambrosia pollen count, even if increasing in Genoa'satmosphere, could still be too low, and it would takesome more time to cause allergic sensitisation in exposed people.This kind of study, pointing out the influence ofairborne allergen exposure on hypersensitivitymechanisms, should be extended in time and world-wideto obtain general conclusions.     

Monitoring of airborne pollen and pollen calendar of Cosenza,Southern Italy

Summary From May 1986 to May 1989 surveys of airborne biological particles have been performed in the atmosphere of Cosenza, Italy with the aim of monitoring the presence of airborne pollen. The survey station is situated at Arcavacata of Rende, a hilly area 474 meters above sea level, 7 km north-west of the main town. The sampler (VPPS 2000) is located about 20 meters above ground level. The monitoring, performed in accordance with the criteria suggested by the Italian Association of Aerobiology (A.I.A.), enabled the identification of 26 different pollen types. The pollination graphics show: 1) a late winter period in which pollen from trees appears; 2) a spring period with a prevalence of Gramineae, Fagaceae, Oleaceae andParietaria pollen; 3) a late spring-summer period during which Fagaceae,Pinus and Compositae pollen grains are present; 4) a late summer-autumn and winter period characterized by a drastic reduction of airborne pollen. A study of the calendar reveals, furthermore, that: 1) Gramineae pollen is, amongst those of allergological importance, the most representative; 2)Parietaria is not perennial and is present in modest concentrations; 3)Olea reaches a high peak in June, but not as high as in other southern regions; 3) pollen from arboreal plants is prevalent compared to that of herbaceous plants.     

Anther opening, pollen biology and stigma receptivity in the long blooming species, Parietaria judaica L. (Urticaceae)

Background and aimsThis paper is about pollen ecophysiology, anther opening, pollen dispersal and the timing of the male and female phases in Parietaria judaica (Urticaceae).MethodsEcophysiological (effects of different relative humidities (RHs) and osmotic relationships) and cytological methods (stigmatic receptivity, pollen viability, histology and histochemistry) were used to determine pollen and pollination features during the long blooming period of this species.Key resultsPollen is dispersed by rapid uncurling of the filament and anther opening. The filament and anther lack cells with lignified wall thickenings, which are usually responsible for anther opening and ballistic pollen dispersal. Instead, dispersal is the result of the sudden movement of the filament. Pollen is of the partially hydrated type, i.e. with a water content greater than 30% at shedding, and readily loses water, and hence viability, at low RH. Pollen carbohydrate reserves differ with season. Starchless grains germinate quickly and are less subject to water loss. Flowers are protogynous, pollen release occurring only after complete cessation of the female phase within an inflorescence.ConclusionParietaria has partially hydrated pollen which differs from typical pollen of this type because of its reduced size and the absence of callose. Because of its low water content at the time of shedding it survives better at higher RH. Dispersal and pollination are adapted to pollen features.     

Transport of airborne Picea schrenkiana pollen on the northern slope of Tianshan Mountains (Xinjiang, China) and its implication for paleoenvironmental reconstruction

The understanding of airborne pollen transportation is crucial for the reconstruction of the paleoenvironment. Under favorable conditions, a considerable amount of long-distance-transported pollen can be deposited far from its place of origin. In extreme arid regions, in most cases, such situations occur and increase the difficulty to interpret fossil pollen records. In this study, three sets of Cour airborne pollen trap were installed on the northern slope of Tianshan Mountains to collect airborne Picea schrenkiana (spruce) pollen grains from July 2001 to July 2006. The results indicate that Picea pollen disperses extensively and transports widely in the lower atmosphere far away from spruce forest. The airborne Picea pollen dispersal period is mainly concentrated between mid-May and July. In desert area, weekly Picea pollen began to increase and peaked suddenly in concentration. Also, annual pollen indices do not decline even when the distance increased was probably related to the strong wind may pick up the deposited pollen grains from the topsoil into the air stream, leading to an increase of pollen concentration in the air that is irrelevant to the normal and natural course of pollen transport and deposition. This, in turn, may lead to erroneous interpretations of the pollen data in the arid region. This study provided insight into the shift in the Picea pollen season regarding climate change in arid areas. It is recorded that the pollen pollination period starts earlier and the duration became longer. The results also showed that the temperature of May and June was positively correlated with the Picea pollen production. Furthermore, the transport of airborne Picea pollen data is useful for interpreting fossil pollen records from extreme arid regions.     

Performance of the Coriolis air sampler,a high-volume aerosol-collection system for quantification of airborne spores and pollen grains

The Coriolis δ air sampler manufactured by Bertin Technologies (France) is a continuous air sampler, dedicated to outdoor monitoring of airborne spores and pollen grains. This high-volume sampler is based on patented Coriolis technology delivering a liquid sample. The air is drawn into a conical vial in a whirling type motion using suction; particles are pulled against the wall by centrifugal force. Airborne particles are separated from the air and collected in a liquid medium. This innovative solution allows rapid analysis by several techniques including PCR assay and serological assay in order to measure the antigenicity/allergenicity of pollen grains and fungal spores. Also, traditional counting of pollen grains or taxa identification by optical microscopy can be done. A study has been carried out by the Health Protection Agency (HPA), Porton Down, UK, to measure the physical efficiency of the Coriolis air sampler. The physical efficiency of the sampler for collection of micro-organism-laden particles of various sizes has been compared with that of membrane filter samplers using the techniques described by ISO 14698-1. The Coriolis was operated simultaneously with membrane filter samplers in a controlled room where they were challenged with uniform-sized particles of different diameters containing bacterial spores. For the larger particle sizes, it was found that the physical efficiency of the Coriolis was 92% for 10-μm particles. The biological performance of the Coriolis in the collection of airborne fungal spores and pollen grains was evaluated in comparison with a Hirst spore trap (one-week tape-on-drum type sampler) which is one of the most frequently used traps in the measurement of outdoor pollen grain concentrations. The advantages and limitations of both technologies are discussed. The Coriolis was operated simultaneously with a Hirst spore trap in the sampling station of Réseau National de Surveillance Aérobiologique, France (RNSA); the pollen grain and fungal spore counts were analysed by optical microscopy. The pollen grain count m⁻³ collected was compared for both devices. The dispersion values were obtained and statistical analysis was carried out. This study shows that the Coriolis air sampler provided equivalent recovery of pollen grain and fungal spores compared with the volumetric trap standard method (not significantly different, W test, α = 0.05). Nowadays, the French-led project, acronym MONALISA, with financial support from the European Commission––Life-Environment (LIFE05 ENV/F/000068), is testing this innovative air sampler in order to measure the antigenicity/allergenicity of the main aeroallergen particles, i.e. Betula (birch), Poaceae (grasses), Parietaria (pellitory), Olea spp (olive tree), and Artemisia (mugwort) pollen grains, and Alternaria (fungal spores) to validate a new approach of monitoring instead of quantifying pollen grains by their morphology. The robustness and efficiency of the MONALISA system is being demonstrated at a national level throughout Europe in eight different countries with different bio-climatic and topography characteristics: France, UK, Finland, Poland, Spain, Portugal, Switzerland, and Italy.     

<Emphasis Type="Italic">Parietaria judaica</Emphasis> flowering phenology,pollen production,viability and atmospheric circulation,and expansive ability in the urban environment: impacts of environmental factors

Parietaria judaica (Urticaceae) grows abundantly in urban areas of the Mediterranean region. Its pollen is a major allergy source. We studied the species’ distribution and abundance in and around Thessaloniki (Greece), pollen production and pollen season. We also examined how urban pollution affects pollen viability. Our ultimate goal was to obtain an estimate of the species’ performance and ability to expand under different environmental conditions related to climate change. We mapped P. judaica and the other Urticaceae species. In a north- and a south-facing population, we recorded the progress of P. judaica flowering and estimated the pollen content per flower, shoot and surface unit. We concurrently assessed atmospheric circulation of Urticaceae pollen. We estimated P. judaica pollen viability and Cu, Pb and Zn concentrations in plants collected from sites differing in traffic intensity. P. judaica is the most abundant Urticaceae species in the area; its occurrence has increased dramatically over the last 100 years. Production of flowers is intense in spring and autumn. Flowering started 12 days earlier in the south-facing population in spring, and 3 days later in autumn. Pollen production was higher in spring and in the south-facing population. Flower and pollen production were positively correlated with the size of the plant and the flower, respectively. Copper and lead concentrations in plants were positively correlated with pollen viability, which was higher for plants collected from high-traffic sites. P. judaica has a high phenotypic plasticity; this is a feature that promotes success of expansive and invasive species. It is also well adapted to warm and polluted urban environments. The climatic change forecast for the Mediterranean region could provoke earlier, longer, and more pronounced flowering and, consequently, more P. judaica pollen in the air. In return, this would result in increased severity of Parietaria pollinosis.     

The main pollen season of Parietaria in Genoa (Italy): forecast possibilities

The authors propose a statistical model for evaluating the Beginning of the Main Pollen Season (BMPS) of Urticaceae (cf. Parietaria) in Genoa (Italy). For eight consecutive years (1981–1988) the mean daily concentrations of this pollen grain were studied in relation to the two meteorological factors which are most significant in triggering the beginning of maximal pollination, namely, mean daily air temperature and rainfall. From a multiple-regression statistical analysis, a formula has been extrapolated, which, one the basis of these meteorological data for the month of January, can be used to predict the onset of the BMPS to within nine days.     

Comparison between Urticaceae (Parietaria) pollen count and hay fever symptoms: assessment of a «threshold-value»

Summary A comparison betweenParietaria pollen count and allergic symptoms of rhino-conjunctivitis in the early season was used in utilized to determine a «threshold-value» for this pollen. Clinical data were obtained from diary-cards of 34 allergic patients and pollen data from a volumetric sampling, carried out by means of a Hirst-Burkard pollen-trap. A significant correlation (r=0.98) was found between pollen count and symptom scores. Mild symptoms were registered with concentrations above 10–15 pollens/m³. Severe symptoms occurred when pollen count exceeded 80/m³/24 h., and over 90% of patients recorded symptoms. The importance of the late reactions and of the total allergenic airborne content are emphasized.     

石家庄市空气花粉散布规律及与气候因子的关系

石家庄市2007—2009连续两年空气花粉分析表明:受植物花期影响,春季以木本植物花粉为主,夏、秋季以草本植物花粉为主,不同类型花粉通量存在一定年际差异。松属、杨属、胡桃属等当地花粉含量占花粉组合的80.0%以上,桦木属、栎属、虎榛子属等区域花粉含量低于20.0%,显示空气花粉能较好地反映周围植被,但也受区域植被的影响。依据空气花粉通量变化规律,石家庄市主要空气花粉类型通量从高到低排在前5位的依次为:胡桃属、悬铃木属、蒿属、杨属、藜科,均为高致敏类型,花粉过敏症患者在其花期或通量较高时期应早作防范。空气花粉百分含量与气候因子之间的(CCA)分析结果显示,其主要受风速与水汽压影响;不同季节主要花粉类型通量与气候因子的相关分析表明:春季和秋季空气花粉通量主要受气温和水汽压的影响,夏季主要受相对湿度和水汽压的影响,冬季与气候因子相关较弱。     

Evaluation of the age of onset of respiratory allergic symptomatology

Summary In order to evaluate the age of ouset of respiratory allergic symptoms we examined 2315 patients (656 children and 1659 adults) coming to our clinic as out patients. Each patient underwent the following diagnostic tests: anamnestic and clinical examination, skin-tests for the most common allergens and, when requested, Radioallergosorbent test (RAST) and specific and non specific BPT.We selected 278 children and 673 adults for whom it was possible to establish (on the basis of precise anamnestic considerations) the age at which the respiratory symptoms first appeared.Among these, 300 reacted only toParietaria pollen, 58 only to grass pollen, 420 only to house-dust mite, and 173 were not allergic.Patients reacting to multiple allergens were excluded from the analysis.The results of our study show a significant precocity of the onset of symptoms related to allergic sensitization to mites with peak level at 5 years.On the other hand, the onset of pollen-related symptoms was later on (peak level at 20–25 years forParietaria pollen and 30–35 years for grass pollen). For non allergic patients we did not find a definite age of onset.     

Towards all-european pollen reports

In the first European Pollenflight Symposium in Königswinter, BRD, March 20–21, in 1987 the outlines for an European data bank were published. By that time Vienna, Austria was already in state of readiness. Since that, countries in Europe have an opportunity to send their prevailing pollen data to the data bank in Vienna, where a software server is ready to accept new data and to send reports day and night. The software of the data bank has been customed to facilitate calculations on PC level. The developing data bank gives a possibility e.g., (1) to compare pollen seasons in various parts of Europe, (2) to make pollen forecasts in different parts of Europe more accurately, (3) to find pollenfree sites in Europe for allergic people, (4) to find out long-time changings in regional and overregional flora as well as in the allergen-content of the air and (5) even to make all-European pollen reports. These could be broadcasted by common satellite TV channels and seen in most European countries. The aim of this study was to compare pollen seasons of the most common allergic symptoms causing plants in Europe: Alnus, Corylus, Betula, Poaceae and Artemisia in 1988 and 1989 and their distribution in Europe. Olea and Parietaria, being widespread pollen allergens in the Mediterranean, have not been taken into consideration for this study in terms of missing data from Spain, southern France and Greece. Information on flowering has been received from Austria, Belgium, BRD, DDR, Denmark, Finland, Italy, The Netherlands, Norway, Poland, Sweden, Switzerland, United Kingdom and the newest site in Estonian SSR. As the number of participating countries is still increasing, (Hungary and France are preparing for joining in 1990), there is no doubt that the need and benefit of a common pollen data bank has been realized in whole Europe.     

The Role of Arabidopsis ABCG9 and ABCG31 ATP Binding Cassette Transporters in Pollen Fitness and the Deposition of Steryl Glycosides on the Pollen Coat

The pollen coat protects pollen grains from harmful environmental stresses such as drought and cold. Many compounds in the pollen coat are synthesized in the tapetum. However, the pathway by which they are transferred to the pollen surface remains obscure. We found that two Arabidopsis thaliana ATP binding cassette transporters, ABCG9 and ABCG31, were highly expressed in the tapetum and are involved in pollen coat deposition. Upon exposure to dry air, many abcg9 abcg31 pollen grains shriveled up and collapsed, and this phenotype was restored by complementation with ABCG9_pro:GFP:ABCG9. GFP-tagged ABCG9 or ABCG31 localized to the plasma membrane. Electron microscopy revealed that the mutant pollen coat resembled the immature coat of the wild type, which contained many electron-lucent structures. Steryl glycosides were reduced to about half of wild-type levels in the abcg9 abcg31 pollen, but no differences in free sterols or steryl esters were observed. A mutant deficient in steryl glycoside biosynthesis, ugt80A2 ugt80B1, exhibited a similar phenotype. Together, these results indicate that steryl glycosides are critical for pollen fitness, by supporting pollen coat maturation, and that ABCG9 and ABCG31 contribute to the accumulation of this sterol on the surface of pollen.     

Pollen viability as a bio-indicator of air quality

Many air pollutants cause plant deterioration. In this study pollen viability was used as bio-indicator of air quality. The study was carried out in the city of Perugia where road traffic is the most important cause of air pollution. Three areas, with different intensity of road traffic (very high, medium and absent) but all characterized by the presence of the same plant species, were selected. Eight species were studied: Hedera helix L., Convolvulus sepium L., Cynodon dactylon (L.) Pers., Quercus ilex L., Dactylis glomerata L., Parietaria diffusa M. et K., Daucus carota L. and Tilia cordata Miller. The pollen of these species was treated with TTC (2, 3, 5 Tryphenil-Tetrazolium-Chloride) staining solution and viability was then estimated by light microscopy. The results showed that the pollen viability was inversely proportioned with pollution. The highest difference in pollen viability between the areas was registered in Tilia cordata. Quercus ilex instead showed that there was no difference in pollen viability between the three different areas. Parietaria diffusa showed a particular behaviour; the highest pollen viability percentage was in polluted areas. The statistical analysis (ANOVA) showed that the main source of variability of the pollen viability depends on the plant but also the site and the interaction between plant and site were very important with a high significant level (p < 0.0001). This revised version was published online in June 2006 with corrections to the Cover Date.     

The partial contribution of specific airborne pollen to pollen induced allergy

The air that we inhale contains simultaneously a multiple array of allergenic pollen. It is well known that such allergens cause allergic reactions in some 15 of the population of the Western World. However little is known about the quantitative aspect of this phenomenon. What is the lowest concentration of pollen that might trigger allergic responses? As people are exposed to heterogeneous and variable environments, clarification of the partial contribution of each of the major airborne pollen allergens and determination of its role in invoking allergy are of prime importance. Objectives: (1) Assessment of a possible correlation between the concentration of airborne pollen and incidence of allergy. (2) Estimation of the lowest average concentrations for various species of airborne pollen that elicit allergic symptoms when exceeded. (3) Determination of the extent of the variations in manifestation of allergy symptoms that can be explained by fluctuations in the concentration of individual species of airborne pollen. Methods: The study was conducted during 14?months with a rural population in Israel. The participants completed a detailed questionnaire and were skin prick tested with the common airborne allergens. The appearance of clinical symptoms, i.e. nasal, bronchial, ocular or dermal, were reported daily by the patients. Concentrations of the airborne pollen and spores were monitored in the center of activity of the residents during one day every week, using three ‘Rotorod’ pollen traps. The pollen grains were identified by light microscopy. Results: The pollen spectrum was divided into time-blocks presenting the main pollination periods of the investigated species. The correlation between the concentration of airborne pollen of the relevant species and the clinical symptoms of the patients was determined for each time block. The correlation differed for different clinical symptoms and for different pollen allergens. Highest correlation with airborne pollen counts was found for patients with nasal and bronchial symptoms. The onset of the clinical symptoms by sensitive patients started, in each of the relevant groups, once the weekly average concentration of the airborne pollen crossed a threshold level. Under the limitations of the present study, this level was estimated to be 2–4 pollen m^?3 air for olive, 3–5 pollen m^?3 air for grasses, 4–5 pollen m^?3 air for Artemisia, 10–20 pollen m^?3 air for pecan and 50–60 pollen m^?3 air for cypress. Conclusions: Fluctuations in specific airborne pollen grains explained up to 2/3 of the variation in clinical allergy responses. Those were: 69 of the variation for cypress (March–April), 66 for the grasses (March–April), 49 for the pecan (May–June) and 62 for Artemisia (Autumn).