Adaptive immunity and memory

The adaptive immune system can recognize particular antigens using lymphocytes. After an initial response, some activated cells become memory cells. On later exposure to the same antigen, memory can support a faster or stronger response. This specificity matters: memory of one antigen does not imply equal protection against every pathogen. Immune responses also involve innate defences. These ideas explain a biological mechanism, not a guarantee about an individual's response to an infection.