Abstract: A lid and a method of testing a test substance in a porous membrane insert (PMI) are dis closed, the lid including a body, sidewalls positioned along an outer perimeter of the body and configured to be seated on a shoulder of a multi-well cell culture plate, and at least one hole through the body and/or at least one knockout, wherein the lid is configured to provide the at least one hole over a corresponding well of the multi-well cell culture plate which contains the porous membrane insert. The method is a method of testing a test substance in a PMI, the method includes the steps of providing a multi-well plate with PMIs, providing the lid, removing the cover from the multi-well plate, adding the test substance, placing the lid on the multi-well cell culture plate, and conducting a manipulation of the test substance.

Abstract: A method of testing a test substance in an in vitro model of a human tracheobronchial respiratory tract, includes: providing the in vitro model including a cell culture including airway epithelial cells (AECs), a basolateral compartment below the AECs and an apical compartment above the AECs, wherein the AECs form a barrier between the basolateral AND apical compartments; adding the test substance to the apical and/or basolateral compartment; adding a tracer to the basolateral compartment, which is fluorescent, has a molecular weight within 5 kDa of human albumin and is added before, during or after adding the test substance; incubating the cell culture system in a presence of the tracer; collecting at least one sample from the apical compartment; and measuring a fluorescence thereof to determine an effect of the test substance on the AECs. A kit is also disclosed.