Figure 3. Basophils and dendritic cells, functioning as antigen-presenting cells, are differentially involved in various T_H2-type immune responses.

Both basophils and dendritic cells (DCs) are involved in the fate determination of naive CD4⁺ T cells through cytokine production and antigen presentation; however, the relative importance of these two cell types seem to be different in various models. a | In papain-induced (and possibly other cysteine protease allergen-induced) T helper 2 (T_H2)-type responses, basophils seem to be crucial, whereas DCs are not essential. Interleukin-4 (IL-4) and thymic stromal lymphopoietin (TSLP), produced by activated basophils, are important for such T_H2 cell differentiation. b | Different Trichuris muris-derived products may simultaneously activate basophils and DCs. Basophils are predominantly involved in T_H2 cell induction, whereas DCs induce both T_H1 and T_H2 cell differentiation. TSLP produced by basophils may be required for suppressing IL-12 production by DCs, promoting the development of T_H2 cell-inducing DCs and inducing IL-4 production by T cells. IL-4 produced either by basophils or T cells is also crucial for inhibiting interferon-γ (IFNγ) production in T cells and amplifying T_H2-type responses. c | In some helminth infection models, helminth products including omega-1 can down-modulate the functions of activated DCs and suppress IL-12 production; therefore, IL-4-independent T_H2 cell differentiation occurs without the involvement of basophils. T_H2-type responses to Nippostrongylus brasiliensis do not require basophils, and such responses are both IL-4 and TSLP independent. PAR, protease-activated receptor; R, receptor; TCR, T cell receptor.