Human basophils lack the capacity to drive memory CD4+ T cells toward the IL-22 response

Mutual Interaction of Basophils and T Cells in Chronic Inflammatory Diseases

Basophils are, together with mast cells, typical innate effector cells of allergen-induced IgE-dependent allergic diseases. Both cell types express the high-affinity receptor for IgE (FcεR1), release histamine, inflammatory mediators, and cytokines following FcεR1 cross-linking. Basophils are rare granulocytes in blood, lymphoid, and non-lymphoid tissues, and the difficulties to detect and isolate these cells has hampered the study of their biology and the understanding of their possible role in pathology. Furthermore, the existence of other FcεR1-expressing cells, including professional Ag-presenting dendritic cells, generated some controversy regarding the ability of basophils to express MHC Class II molecules, present Ag and drive naïve T cell differentiation into Th2 cells. The focus of this review is to present the recent advances on the interactions between basophils and peripheral blood and tissue memory Th1, Th2, and Th17 cells, as well as their potential role in IgE-independent non-allergic chronic inflammatory disorders, including human inflammatory bowel diseases. Basophils interactions with the innate players of IgE-dependent allergic inflammation, particularly innate lymphoid cells, will also be considered. The previously unrecognized function for basophils in skewing adaptive immune responses opens novel perspectives for the understanding of their contribution to the pathogenesis of inflammatory diseases.

Basophils are inept at promoting human Th17 responses

Basophils are the rare granulocytes and play an important role in the polarization of Th2 responses and protection against helminth parasites. In addition, basophils contribute to the pathogenesis of several diseases such as asthma, chronic allergy and lupus. Notably, Th17 cells are also implicated in the pathogenesis of these diseases suggesting that basophils support the activation and expansion of this subset of CD4(+) T cells. Therefore, we explored whether basophils promote the expansion of human Th17 cells. We show that basophils lack the capacity to expand Th17 cells and to induce the secretion of Th17 cytokines either directly or indirectly via antigen presenting cells such as monocytes. As human basophils lack HLA-DR and co-stimulatory molecules, their inability to confer T cell receptor- and co-stimulatory molecule-mediated signals to CD4(+) T cells might explain the lack of Th17 responses when memory CD4(+) T cells were co-cultured with basophils.