section_path: Adaptive immune system/Immunological memory
section_name: Immunological memory
paragraph_text: Immunological memory
  
  When B cells and T cells are activated and begin to replicate, some of their offspring become long-lived memory cells. Throughout the lifetime of an animal, these memory cells remember each specific pathogen encountered and can mount a strong response if the pathogen is detected again. T-cells recognize pathogens by small protein-based infection signals, called antigens, that bind to directly to T-cell surface receptors. B-cells use the protein, immunoglobulin, to recognize pathogens by their antigens. This is "adaptive" because it occurs during the lifetime of an individual as an adaptation to infection with that pathogen and prepares the immune system for future challenges. Immunological memory can be in the form of either passive short-term memory or active long-term memory.