Cutting edge: biasing immune responses by directing antigen to macrophage Fc gamma receptors.

An immune response can deviate toward either a Th1- or Th2-like response. In this work we examine the contribution that activated macrophages and IgG Abs make toward this deviation. The use of activated macrophages as APCs resulted in a strong polarized T cell response that was predominated by IFN-gamma. However, when Ag was targeted to FcgammaRs on these macrophages, the T cell response was reversed and biased toward a Th2-like response. This Th2-like phenotype was stable and was retained when the T cells were subsequently restimulated under nonbiasing conditions. The T cell biasing and its reversal via FcgammaR was also observed in vivo. Mice vaccinated with IgG-opsonized OVA made high levels of IgG Ab of the IgG1 isotype. These studies demonstrate that the ligation of FcgammaR on activated macrophages can reverse the Th1 biasing that occurs as a result of innate immune responses to microbial products.