Those who are exposed to large quantities of airborne allergens can develop a serious inflammation of the lungs known as alveolitis. In this disorder it is not the tubes leading to the lung that are affected (as in asthma) but the lungs themselves. Tiny air-sacs known as alveoli perform the actual work of the lung in extracting oxygen from the air and passing it to the blood. If an allergic reaction to airborne allergens occurs in the alveoli, the large number of immune complexes produced can be deposited there and cause highly damaging inflammation. The structure of the alveoli begins to break down, causing shortness of breath,-tightness in the chest, fever and a dry cough.
There are several forms of alveolitis including farmer’s lung and mushroom-worker’s lung, but the only one likely to have any relevance to food allergy is bird-fancier’s lung. In this disorder, it is tiny particles from the birds’ droppings that initiate the allergic reaction in the alveoli. The connection with food allergy is a tenuous one, but some doctors claim that eating eggs can exacerbate the symptoms in a few patients. This might occur if the antibodies produced to the antigens in the droppings also bind to antigens from egg proteins carried in the bloodstream. This dual binding – known as cross-reactivity – can occur where antigens are chemically similar. Laboratory experiments suggest that there is cross-reactivity between the antigens of chicken’s eggs and the antigens found in the droppings of budgerigars and pigeons.