Final answer:
The immune system recognizes new antigens based on their immunogenicity, with B and T cells generating receptors capable of binding a vast array of antigens through genetic rearrangement. The primary adaptive response creates a memory that leads to a faster, stronger secondary response upon subsequent exposures.
Step-by-step explanation:
When the immune system encounters a completely new antigen, it recognizes it as a potential pathogen based on the antigen's immunogenicity, which refers to the ability of the antigen to elicit an immune response. As part of the adaptive immune response, B cells and T cells have receptors that can bind to a wide variety of antigens due to a genetic mechanism that allows for a vast array of receptor specificities. This enables the immune system to recognize and combat pathogens that it has not previously encountered. Through a process that involves the rearrangement of gene segments, as many as 1011 or 100 trillion different receptors can be generated, providing the specificity required to identify new antigens.
The initial response of the immune system to a pathogen is known as the primary adaptive response, and although this first response might take time to become effective, it provides the basis for immunological memory. On subsequent exposure to the same pathogen, a faster and stronger secondary adaptive immune response occurs, which protects us from many diseases by preventing the pathogen from causing significant damage or symptoms. This immunological memory is a key feature of the adaptive immune response.