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Why can antiserum provide immediate protection against some toxins or microbes?

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Diagram of an antibody molecule showing two identical light chains and two identical heavy chains joined by disulfide bonds in a Y-shaped structure, with labeled regions for antigen binding and effector function. — antibody The four-chain structure of an antibody, or immunoglobulin, molecule. The basic unit is composed of two identical light (L) chains and two identical heavy (H) chains, which are held together by disulfide bonds to form a flexible Y shape. Each chain is composed of a variable (V) region and a constant (C) region.

Antiserum provides immediate protection because it contains preformed antibodies that have already been generated by another individual or animal in response to a specific antigen.123

When a person is exposed to a fast-acting toxin or a dangerous microbe, their own immune system may not have enough time to mount an effective response. By administering antiserum, the patient receives a concentrated dose of these ready-made antibodies, which can immediately begin to neutralize the threat. These antibodies work by binding directly to the toxins or pathogens, rendering them harmless, preventing them from invading body cells, or marking them for destruction by the body's immune cells.21435

This process is known as passive immunization, as it bypasses the need for the recipient's body to produce its own antibodies. While this provides life-saving, immediate assistance, it is temporary because the body eventually breaks down the foreign antibodies.26