Macrophage IL-4 polarization is restricted by soluble CD40 agonists and antigen-induced CD154 but not by constitutive...

Stimulation of macrophages via CD40 promotes their classical activation. Therefore, CD154 (CD40 ligand) can be expected to oppose macrophage polarization and proliferation induced by IL-4. However, there are limited experimental data to support this, which is additionally complicated by the possibility of differential effects of CD40 agonists in different formats/contexts. Whereas canonically CD4+ T cells upregulate CD154 strongly following exposure to cognate antigen, naïve CD4+ cells constitutively express significant levels of CD154, which could be a tonic signal. Soluble CD154 and agonistic CD40 antibodies also trigger CD40 signaling. We explored these questions in a reductionist model of IL-4 delivery to mouse peritoneal cavity cells in vitro and in vivo. Soluble CD40 agonists inhibited M(IL-4) polarization, with a stronger effect on RELM-α than on Ym1 (Chil3), as well as inhibiting IL-4-induced proliferation. CD154 provided by CD4+ cells in the context of an antigen-specific interaction blunted macrophage RELM-α expression but did not affect Ym1. Macrophages negatively regulated, via CD40, constitutive cell-surface CD154 on naïve CD4+ cells, both in vitro and in vivo. The large peritoneal macrophages of CD40 KO mice showed a moderately enhanced RELM-α response to IL-4, but this was not a cell-autonomous effect. No differences between WT and CD40 KO mice were detected in IL-4-induced macrophage proliferation. We conclude that strong CD40 stimulation, including stimulation by CD154 expressed by antigen-specific CD4+ cells, blunts selected macrophage responses to IL-4, and that constitutive CD4+-cell CD154, in spite of interacting with CD40 on macrophages, does not directly influence macrophage responses to IL-4.