Fc-γ Receptors efficiently internalize antigen-antibodies (Ag-Ab) complexes and thus induce processing of antigens into peptides presented by MHC class II molecules. The recognition of p-MHC complex by T-cell receptor (TCR) trigger further immune reactions. It is still unclear how antigen binding in antibody and p-MHC binding in TCR communicate allosterically with their receptor bindings, respectively. The CDRs are responsible for Ag recognition, while the constant domains are crucial to activate effector function. To study the allosteric effects of antigen binding, we simulated four complex structures of free antibody, antigen bound antibody, FcR bound antibody, and antigen-antibody-FcR complex. As the conformation dynamics of antibodies are critical to antibody function, we chose 12 independent initial conformation to enhance the sampling. We reproduced experimental domain distribution density for the apo antibody, with the two Fabs move highly dynamic around the Fc region with Fab and Fc domains constantly forming and breaking contacts. When bind to antigen, the antibody conformation shift to two dominant conformation clusters, with one cluster has Fc-receptor binding site widely open. The final binding of Fc-γ Receptors leads to two conformation clusters, one corresponding to the antigen-free antibody-FcR baseline binding, and one for stronger antigen enhanced antibody-FcR interaction. Structural analysis of the antigen-antibody-FcR complex suggested that the antigen binding signal can transferred from the CDRs to the FcR by two main pathways, i.e. through hinge region and CH1/CL region. The results suggested that the stable contacts between CH1/CL and FcR is important for the transfer of antigen binding signals. Our study revealed the atomic mechanisms of the allosteric communications connection the antibody-antigen recognition and following FcR activation. During these processes, antigen binding shifts the antibody conformations which facilitate the FcR binding as well as allosteric signal transfer.