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Eur. Cytokine Netw., Vol. 21 n° 3, September 2010, 142-53


Basophils: new players in the cytokine network
Elke Schneider, Nathalie Thieblemont, Maria Leite De Moraes, Michel Dy
CNRS UMR 8147 “Cytokines, Hematopoiesis and Immune Responses”, Faculté de Médecine Université Paris-Descartes, Hôpital Necker, Paris, France Correspondence: Dr M. Dy, CNRS UMR 8147 “Cytokines,Hematopoiesis and immune response”, Hopital Necker, 161, rue de Sèvres, 757433 Paris Cedex 15, France Accepted for publication April 8, 2010

ABSTRACT. Basophils belong to a myeloid cell population that has been ignored for more than a century, mainly because of its paucity, its lack of specific markers, and the absence of experimental models. Given that in mice, even the mere existence ofbasophils was contested, they were alluded to as “histamine-producing cells” or “non-T non-B cells” in initial studies. It is now widely acknowledged that basophils respond to various IgE-dependent or -independent stimuli, and are engaged in a complex cross talk with a number of immunocompetent cells (T or B lymphocytes, macrophages, dendritic cells, endothelial cells…). Indeed, on the one hand theyare critically involved during the onset, the effector phase and exacerbation of TH2 responses through their capacity to generate large amounts of cytokines with pro-TH2 functions (IL-4, IL-13 TSLP, IL-25), on the other hand, they contribute to immunoglobulin synthesis and class switching, angiogenesis, autoimmunity, tumor immunity and hematopoiesis by producing cytokines such as IL-6, VEGF, GM-CSFand IL-3. Finally, it has been established that they can present antigens to CD4+ or CD8+ T cells in an MHC class II- or class I-dependent manner, respectively. Taken together, these activities confer important immunoregulatory functions upon basophils, both in innate and adaptive immunity.
Keywords: basophils, histamine, IL-4, immunoregulation, TH2 responses, allergy

Although Paul Ehrlichidentified basophils only two years after mast cells in 1879 [1], this cell population was then neglected or ignored for more than a century, and was often mistaken as a circulating form of mast cells. Indeed, basophils are the least common granulocytes in the circulation, where they usually represent less than 1% of the white blood cell population. Furthermore, the absence of specific surfacemarkers, at least in mice, has been a drawback to their purification. Progress in basophil research has also been hampered by apparent morphological and functional redundancies with mast cells and the lack of suitable murine experimental models, which explains why immunologists have taken little interest in this field. Indeed, although basophils are found in most vertebrates (mammals, birds, reptilesand amphibians), as well as in fish [2], with some variations as to their number and morphological features, in mice even their very existence was doubted until quite recently. This erroneous notion originated from the differences between murine and human basophil morphology, the former being markedly less granulated than the latter. Human basophils have only been recognized as the unique source ofhistamine among blood leukocytes since 1955 [3], while histamine synthesis in their murine counterpart was first reported in 1981, in response to a cytokine initially termed histamine-producing cell stimulating factor (HCSF) [4] that was later identified as IL-3 [5]. The corresponding biological activity, called HCSA (histamine-producing cell stimulating activity) [6, 7], was

initiallydescribed in a model of allograft rejection, but was demonstrated later during anti-parasitic or mitogenic responses [4, 8, 9]. It resulted from a small subset of bone marrow cells originally named histamine-producing cells that have since been characterized as basophils [10]. Immunologists came to recognize basophils as potential immunoregulatory cells only when it was discovered that they represent...