Alloimmune, or isoimmune, neutropenia of newborns occurs in the fetus due to antigenic incompatibility of the fetus's and mother's neutrophils. The mother's isoantibodies belong to the IgG class, they penetrate the placental barrier and destroy the child's neutrophils. Isoantibodies are usually leukoagglutinins, they react with the cells of the patient and his father, do not react with the mother's cells.