Immunity

Immunity acquired by directly receiving preformed antibodies, rather than by producing them in one's own body, is called passive immunity, and it provides rapid but short-lived protection. When a person is exposed to a deadly toxin such as in tetanus or snakebite, preformed antitoxin antibodies are injected so that they neutralise the toxin immediately, since the body has no time to mount its own slower antibody response. Active immunity is incorrect because it develops only when the host's own immune system is stimulated by a live antigen or vaccine to manufacture antibodies, a process that takes time. Innate immunity is wrong because it is the non-specific, inborn defence present from birth, such as skin barriers and phagocytes, and does not involve injected antibodies. Cell-mediated immunity is incorrect since it is driven by T-lymphocytes attacking infected cells rather than by transferring ready antibodies. As explained in NCERT Class 12, Chapter 8 (Human Health and Disease), the antibodies passed from mother to foetus through the placenta and through colostrum are natural examples of passive immunity. As a consistency check, because no host antibody synthesis is required and protection is instant, the described scenario can only represent passive immunity.