Activation of human eosinophil effector functions by CC chemokines

Establishment of experimental eosinophilic vasculitis by IgE-mediated cutaneous reverse passive arthus reaction

Prominent eosinophil infiltration is a characteristic of some forms of vasculitis, such as Churg-Strauss syndrome, also known as allergic granulomatous vasculitis. In the current study, we established a mouse model of cutaneous eosinophilic vasculitis by the cutaneous reverse passive Arthus reaction using IgE injection instead of IgG. Wild-type C57BL/6 mice were injected with IgE anti-trinitrophenyl antibodies, followed immediately by intravenous administration of trinitrophenyl bovine serum albumin. IgE-mediated immune complex challenge induced substantial hemorrhage with marked infiltration of eosinophils in which neutrophils, mast cells, and macrophages were also mixed. This finding contrasted remarkably with the neutrophil-dominant infiltration pattern in IgG-mediated immune complex challenge. In the lesion, the expression level of monocyte chemotactic protein-3 was increased, and anti-monocyte chemotactic protein-3 treatment resulted in a significant but incomplete blockade of eosinophil recruitment. Furthermore, mice lacking E-selectin, P-selectin, L-selectin, or intercellular adhesion molecule-1, as well as wild-type mice that received anti-vascular cell adhesion molecule-1-blocking antibodies were assessed for the IgE-mediated Arthus reaction. After 24 hours, the loss of P-selectin resulted in a significant reduction in eosinophil accumulation compared with both wild-type mice and other mouse mutants. Collectively, the Fc class of immunoglobulins, which forms these immune complexes, critically determines the disease manifestation of vasculitis. The IgE-mediated cutaneous reverse passive Arthus reaction may serve as an experimental model for cutaneous eosinophilic infiltration in vasculitis as well as in other diseases.

Cytokine-regulated accumulation of eosinophils in inflammatory disease

The role of cytokines in the accumulation of eosinophil granulocytes in inflamed tissue has been studied extensively during recent years, and these molecules have been found to participate throughout the whole process of eosinophil recruitment. Haematopoietic cytokines such as IL-3, IL-5 and GM-CSF stimulate the proliferation and differentiation of eosinophils in the bone marrow, and the release of mature eosinophils from the bone marrow into the blood is probably promoted by IL-5. Priming of eosinophils in the blood following, for example, allergen challenge is performed mainly by IL-3, IL-5 and GM-CSF. An important step in the extravasation of eosinophils is their adhesion to the vascular endothelium. Adhesion molecules are upregulated by, e.g. IL-1, IL-4, TNF-alpha and IFN-gamma and the same cytokines may also increase the affinity of adhesion molecules both on eosinophils and endothelial cells. Finally, a number of cytokines have been shown to act as eosinophil chemotactic factors, attracting the cells to the inflammatory focus in the tissue. Some of the most important eosinophil chemoattractant cytokines are IL-5, IL-8, RANTES, eotaxin, eotaxin-2, eotaxin-3, MCP-3, MCP-4 and TNF-alpha. Th2 cells, mast cells and epithelial cells are important sources of proinflammatory cytokines, but in recent years, the eosinophils have also been recognized as cytokine-producing and thereby immunoregulatory cells. The aim of this paper is to review the role of cytokines in the process of eosinophil recruitment in asthma, allergy and ulcerative colitis.

Eosinophils, eosinophilic cytokines (interleukin-5), and antieosinophilic therapy in asthma

Eosinophils are believed to be key effector cells in producing the bronchial mucosal inflammation characteristic of allergic asthma. Given the perceived importance of eosinophils in allergic inflammation, they have been logical therapeutic targets. As knowledge of eosinophil biology increases, eosinophils are targeted with specific therapies blocking their maturation, activation, and chemotaxis. Therapeutic targets include eosinophil-specific cytokines, primarily interleukin-5, and chemokines, eg, eotaxin. Several studies over the last year have reported on therapies effective at reducing eosinophil numbers in asthmatics, including two humanized monoclonal antibodies against interleukin-5 and recombinant human interleukin-12. Surprisingly, despite their effectiveness at depleting eosinophils, there was no evidence of clinical improvement in any of the parameters studied. These and all other relevant studies published within the last year are reviewed by this article. After publication of these studies, some commentators questioned the role of eosinophils in allergic inflammation. Current evidence for and against eosinophils as effector cells in asthma is reviewed.

Migration of helper T-lymphocyte subsets into inflamed tissues

The localization of lymphocytes to specific tissues is a finely regulated event that has key implications in the development of chronic allergic inflammation that is associated with allergic rhinitis, atopic dermatitis, and asthma. Key players in the tissue localization of lymphocytes and other allergic effector cells include cellular adhesion molecules and chemokines. The expression or activation pattern of these proinflammatory mediators appears to depend, in part, on the local cytokine milieu. For instance, the T(H)1 phenotype is associated with the upregulation of intercellular adhesion molecule-1 and RANTES, whereas the T(H)2 phenotype is associated with the upregulation of vascular cell adhesion molecule and P-selectin. Notably, the recruitment of certain cell populations, such as eosinophils (hallmark of chronic allergic inflammation), into inflamed tissue sites is dependent on the preferential expression of adhesion molecules, chemokines, and associated receptors. The potential mechanisms that underlie cell migration into inflamed tissue as currently understood are reviewed.