A membrane permeability test for the detection of cell surface antigens

A convenient microtest is described which utilizes antibody-mediated release of [14C]nicotinamide ([14C]NA) from target cells for the detection of cell surface antigens. This test is considerably more sensitive and faster than the widely used 51Cr release test because most of the [14C]NA is rapidly released from the target cells in the initial phase of membrane permeability changes induced by activated complement, as distinct from the colloid osmotic phase of complement-mediated cytolysis.