A human Fc receptor-specific monoclonal antibody is disclosed together with its mode of preparation. Binding of the antibody to Fc receptor is not blocked by human immunoglobulin G. The antibody binds to the high affinity Fc receptor for IgG on human monocytes at a receptor binding site distinct from the ligand binding site for Fc. A bifunctional antibody or a heteroantibody has an antigen binding region derived from an anti-Fc receptor antibody and an antigen binding region specific for a target epitope or cell; such antibody may target a macrophage when it is bound to surface Fc receptors of the macrophage. A target-specific effector cell expresses receptor for the Fg portion of IgG, has one antigen binding region derived from an anti-Fc receptor antibody and another specific for a target cell, and the aforesaid bifunctional or hetero-antibody is bound to the Fc receptor of the effector cell; such effector cell can be used in the therapy of cancers, allergies, infectious and autoimmune diseases, and in immunoassays.