Abstract: The present invention relates to an immunoactive composition of matter having the general formula AB(T) where AB is an antigen, growth factor or other material which binds to receptor sites on epithelial target cells, notably choroid plexus cells, and T is a moiety which affects the activity of the target cell, for example a toxin or medicament, and which is attached, notably by one or chemical linkages, to the moiety AB. The immunoactive material selectively attaches to the epithelial cells and the moiety T then is absorbed by those cells, thus reducing the risk of acting on other cells. The invention also provides a method of treating epithelial cells, notably the choroid plexus cells so as to regulate the production of CSF from those cells in the treatment of hydrocephalus, by administering the immunoactive material by injection or infusion into the CSF circulation system so as to localise the administration and action of the immunoactive material.