FOREWORD
It is well over a century since Paul Ehrlich was credited with the first recognition and description of the eosinophil as a distinct type of leukocyte. The eosinophil's distinguishing feature then was its affinity for staining with acid aniline dyes, such as eosin, a property that accounts for its name. We now know that dyes such as eosin bind to cationic proteins in eosinophil specific granules, granules whose ultrastructural morphology is unique because of their content of crystalloid cores rich in major basic protein. Curiously, there has been no singularly eosinophilspecific cell surface marker recognized to date; and the identifying features of eosinophils principally remain their morphologic and tinctorial properties visible by light microscopy and their granule ultrastructure visible by electron microscopy. The eosinophil is not unique to mammals but extends, at least based on ultrastructure, well into more primitive animals, including reptiles.
What are the functions of this phylogenetically conserved leukocyte? Answers to this question and even more compellingly to questions about the roles of eosinophils in human diseases associated with eosinophilia, including allergic and parasitic diseases, have prompted a sustained series of studies over the last century. In the 1960's, a couple of research groups began to link eosinophil production with lymphocytes. Major amongst these groups was that headed by Paul Beeson, MD, then at Oxford. In a series of classic studies, Beeson's group established the lymphocyte dependence of heightened eosinophil production (A Basten & PB Beeson 1970. Mechanism of eosinophilia. II. Role of the lymphocyte. J Exp Med 131: 1288-1305). These studies, based in part on unnatural intravascular adminstration of Trichinella larvae in the rat, presaged the later recognition by Sanderson of IL5 as a major eosinophilopoietic cytokine and helped set the stage for resolving lymphocyte functioning into subsets, including Th1 and Th2 subsets.
Dr Beeson brought to his investigations a broad clinical and scientific knowledge. He was well aware of the disease associations of eosinophilia. He remembered the time when lymphocytes were illunderstood and recognized simply as a unitary type of small compact mononuclear leukocytes. Modern immunology has refined, and continues to delineate, the functional diversity and complexity of lymphocytes, despite their nominal morphologic similarity and simplicity. Dr Beeson, a pioneer in laying the groundwork for much of our current studies of eosinophils, has wondered whether the morphologic unity of eosinophils belies a greater diversity of functions for this distinct leukocyte analogous to what has been revealed for the lymphocyte. What are the evolutionary benefits to having eosinophils? A potentially beneficial role in the hostdefense against principally multicellular helminthic parasites has been questioned based on small animal studies ablating eosinophilia with antiIL5. Concurrently, increasing evidence has accumulated linking eosinophils to the pathophysiology of asthma and allergic diseases. What then is the evolutionary benefit for this cell type associated with morbidity and mortality as in asthma? More immediately, how can we understand and therapeutically intervene to control the deleterious actions of eosinophils in such diseases? Are there roles for eosinophils in immune or other responses where there are not obviously increased numbers of eosinophils?
There are many questions one may still raise about the scope of eosinophil functions, but there are also continuing new insights concerning eosinophils. The International Symposium on Eosinophils in Allergic Inflammation and Parasitic and Infectious Diseases, held in Rio de Janeiro, Brazil in 1996 under the auspices of the Minister of Health of the Foundation Oswaldo Cruz and the Institutue Oswaldo Cruz, convened a multitude of international investigators who have been contributing to defining the functions of eosinophils. The proceedings of these meetings provide highly contemporary information on a broad range of related topics pertinent to eosinophils. Much has been learned. New methods, new molecules and new insights have been identified. All answers are not yet in, but the new knowledge reflected in the contributions at this Symposium provides valuable advances in our ongoing investigations of eosinophils and sets the stage for yet further advances in our understanding of the roles and functions of this curious minority leukocyte.
Peter F Weller, MD
Organizer
Publication Dates
-
Publication in this collection
23 Nov 2000 -
Date of issue
Dec 1997
