Treponema pallidum immobilization (TPI) test. Syphilitic spirochetes can grow in rabbits. Nelson devised a Treponema pallidum immobilization (TPI) test in which syphilitic spirochetes are incubated with the patient’s serum. If specific antisyphilitic antibody is present, it will attack the spirochetes and immobilize them, causing them to stop moving when viewed under the microscope. This involves […]