The immunity acquired as a result of an injection of tetanus antitoxin is termed _____ immunity.

The immunity acquired through an injection of tetanus antitoxin is classified as artificially acquired passive immunity. This type of immunity occurs when antibodies are transferred to an individual from another source, in this case, through the administration of the antitoxin.

Tetanus antitoxin contains pre-formed antibodies that provide immediate protection against the tetanus toxin, but it does not stimulate the recipient's immune system to produce its own antibodies in the long term. This is what distinguishes passive immunity from active immunity; in active immunity, the body develops its own immune response to an infection or through vaccination, leading to long-lasting protection.

In contrast, natural immunity refers to the immunity developed through natural exposures to pathogens, which involves the body’s own immune cells generating a response. Artificially acquired active immunity involves vaccination, where a weakened or inactivated pathogen is introduced to stimulate antibody production. Innate immunity, on the other hand, is the body’s initial, non-specific defense mechanism and does not involve antibodies at all.

Therefore, because the tetanus antitoxin provides immediate protection through the transfer of pre-formed antibodies rather than through direct stimulation of the immune system, it is correctly classified as artificially acquired passive immunity.