[New light shed on the enigmatic eosinophilic granulocyte. Both a friend and an enemy]

Eosinophils normally constitute only a few per cent of circulating leucocytes, though they are more numerous in tissues vulnerable to attack by environmental micro-organisms. Eosinophils can kill invasive parasites, but also possess immunoregulatory functions and may be involved, for example, in the connective tissue remodelling that occurs in conjunction with inflammation. Although their effects may be beneficial to the host, for instance in the event of helminthic infestation, they may also cause tissue damage, for example in allergy and asthma. Recent years have witnessed manifest advances in our knowledge of these fascinating but still enigmatic cells.