Abstract: A method for filtering blood is disclosed that in one embodiment includes the steps of depositing unfiltered blood along at least one side of a semi-permeable surface having multiple pores, depositing target tissue along at least an opposing side of the semi-permeable surface, and permitting the unfiltered blood to flow at least partially along the semi-permeable surface to filter the unfiltered blood. Embodiments of the invention can remove self-directed autoantibodies from the blood while reducing the complications of conventional treatments such as plasmaphoresis, and return the patient's own blood cells and its plasma components, less the disease-causing self-directed antibodies. A blood filter and a blood bag are also disclosed.