Stress and allergy.

In recent years it has been seen that the nervous and immune systems regulate each other reciprocally, thus giving rise to a new field of study known as psychoneuroimmunology. Stress is defined as a general body response to initially threatening external or internal demands, involving the mobilization of physiological and psychological resources to deal with them. In other words, stress is characterized by an imbalance between body demands and the capacity of the body to cope with them. The persistence of such a situation gives rise to chronic stress, which is the subject of the present study, considering its repercussions upon different organs and systems, with special emphasis on the immune system and--within the latter--upon the implications in relation to allergic disease. Activation of the neuroendocrine and sympathetic systems through catecholamine and cortisol secretion exerts an influence upon the immune system, modifying the balance between Th1/Th2 response in favor of Th2 action. It is not possible to affirm that chronic stress is intrinsically able to cause allergy, though the evidence of different studies suggests than in genetically susceptible individuals, such stress may favor the appearance of allergic disease on one hand, and complicate the control of existing allergy on the other.

Air pollution and allergens.

It is well known that the prevalence of allergic diseases has increased in recent decades in the industrialized world. Exposure to environmental pollutants may partially account for this increased prevalence. In effect, air pollution is a growing public health problem. In Europe, the main source of air pollution due to particles in suspension is represented by motor vehicles--particularly those that use diesel fuel. Diesel exhaust particles (DEPs) are composed of a carbon core upon which high-molecular weight organic chemical components and heavy metals deposit. Over 80% of all DEPs are in the ultrafine particle range (< 0.1 pm in diameter). Air pollutants not only have a direct or indirect effect upon the individual, but also exert important actions upon aeroallergens. Pollen in heavily polluted zones can express a larger amount of proteins described as being allergenic. Through physical contact with the pollen particles, DEPs can disrupt the former, leading to the release of paucimicronic particles and transporting them by air--thus facilitating their penetration of the human airways. Climate change in part gives rise to variations in the temperature pattern characterizing the different seasons of the year. Thus, plants may vary their pollination calendar, advancing and prolonging their pollination period. In addition, in the presence of high CO2 concentrations and temperatures, plants increase their pollen output. Climate change may also lead to the extinction of species, and to the consolidation of non-native species--with the subsequent risk of allergic sensitization among the exposed human population. In conclusion, there is sufficient scientific evidence on the effect of air pollution upon allergens, increasing exposure to the latter, their concentration and/or biological allergenic activity.