What are the three steps involved in an acquired immunity response to a foreign substance?

• A. Transcription, Dissemination, Response
• B. Processing, Replication, Response
• C. Recognition, Processing, Response
• D. Activation, Recognition, Response

Answer: (C)

The main idea is how the adaptive immune system handles a foreign substance in three coordinated stages: recognition, processing, and response.

First, recognition happens when specialized lymphocytes detect a non-self antigen through their receptors. This step is highly specific—the receptors bind only to particular shapes on the antigen, signaling that a threat is present.

Next comes processing. Antigen-presenting cells digest the captured antigen and display its fragments on MHC molecules. This processing links the detected signal to the appropriate lymphocytes, enabling targeted activation of B cells and T cells.

Finally, the response is executed. Activated B cells produce antibodies to neutralize or mark the invader, while helper and cytotoxic T cells coordinate and carry out cellular attacks. Memory cells are formed as well, so a faster and stronger response occurs if the same antigen is encountered again.

This sequence—recognition, processing, then response—best captures the flow of an acquired immune response to a foreign substance.