Antibody

Antibodies formed part of the immune system of a lifeform, fighting off foreign bodies and preventing disease. Several species applied this concept to machines.

The Great City of the Exxilons created antibodies to defend itself. (TV: Death to the Daleks)

The human-crewed robotic ship, Teselecta, which fittingly appeared as a humanoid, was guarded by an internal system of antibodies which eliminated unauthorised personnel. (TV: Let's Kill Hitler)

The Dalekanium casings which housed the Daleks were similarily protected by a system of antibodies which, as described the Twelfth Doctor, "hoovered" miniaturised intruders into liquid protein which was transferred into the Dalek's feeding tubes. (TV: Into the Dalek)

According to Alistair Gryffen the Alien immunologists Charles and Marie Sobol were the only humans who have ever experimented with alien antibodies and tried to use them for the human immune system. They experimented on themselves and on their child. This granted them an alien immune system. Their blood plasma built alien antibodies and they had an immune response to alien diseases. However, they disappeared years before 2050 without a trace. (TV: Oroborus)

K9 Mark 2 had living metal antibodies which were capable of defending him from 99% of 2050-vintage terrestrial weaponry. (TV: The Last Precinct)