The present application provides the medicaments comprising the antibodies binding to phospholipase D4 (PLD4 ) as well as a method using said medicaments for detecting and suppressing activated B cells. The present application is further directed to therapy of auto immune diseases and allergosis resulting from the active repressing function. In order to solves these problems the present application provides that a monoclonal antibody binding to the extracellular domain of phospholipase D4 (PLD4) protein or a fragment containing an antigen binding region thereof as an active ingredient.
