(iii) By using combined fractions from wild-type and IL-4 -/- mice we demonstrated that Mac-1+, but not CD4+ or CD4−/Mac-1−, cells are essential for IL-4 and IgE Ab production in lymphocytes. Also in the TGF-beta inhibitor present study, Mac-1+/CD3−/IgM−/B220−/CD11c−/CD14−/Ly-6G−/CCR3− cells in the macrophage-rich fraction were crucial for production of IL-4 and IgE Abs (Figs. 5 and 6) or IgG Abs (Fig. 7) by lymphocytes after i.n. sensitization with cedar pollen or this allergen and complete Freund’s adjuvant. Although a large amount of IgE was induced

by one i.n. injection of allergen alone (Fig. 4), the titer relative to high-titer IgE Ab was less than 0.00001 unit/mL (data not shown), revealing the increase to be due to nonspecific IgE Abs, as reported previously (7). Therefore, it is unlikely that the Mac-1+ Alectinib in vivo mononuclear cells (Fig. 6) simply took up and processed protein antigens to present them to T cells. It has been established that bacterial LPS, which can activate B cells independently of antigen, induce formation of a variety of Ig isotypes with the exception of IgE (29). However, when the same B cells are cultured for 5 days with LPS together with 100 to 500 units/mL of IL-4, the result is the formation of IgE and selective enhancement of IgG1 formation (30), which is accompanied by a decrease in IgG2b and IgG3 formation. IL-4, essential for either conversion

of Th0 to Th2 (31) or class switch of IgM to IgE (32), is produced by T cells, mast cells, basophils, eosinophils, and macrophages (33–36). In our mouse model system, CD3+ cells in the submandibular lymph nodes from mice that had been i.n. sensitized once with the allergen alone seemed to be the main producers of IL-4 (Fig. 10). However, the lymphocyte-rich fraction alone was inefficient in production of IL-4 or IgE

(or IgG); addition of Mac-1+ cells from the macrophage-rich fraction to the lymphocyte-rich fraction was essential for this production (Figs. 5–7). Furthermore, a combination of the lymphocyte-rich population (for IgG [or IgE] production) with the macrophage-rich population (for IgE [or IgG] production) produced a large amount of IgE (or IgG). These results N-acetylglucosamine-1-phosphate transferase imply that Mac-1+ mononuclear cells might be involved in recognition of allergenic molecules as nonself (or allergen) and in class switching of Ig in B lymphocytes by controlling the amounts of IL-4 released from T lymphocytes. Specific activation of an antigen-binding B cell (an antigen-presenting cell) by its cognate T cell leads to expression of CD40 ligand on the helper T-cell surface and to secretion of IL-4, IL-5, and IL-6, which drive proliferation and differentiation of B cells into antigen-specific Ab-secreting plasma cells (37). However, as reported previously (7, 8) and also in the present study, the IgE Ab produced by mice that have been injected once i.n. with allergen is not specific for that allergen: the titer relative to high-titer serum was less than 0.