Immunity – we think of uniform system composed of many cell types. In reality, our immune system is divided into two sides of a coin: the innate and the adaptive. Understanding their differences is essential for understanding the mechanistic immunology. 

𝗜𝗻𝗻𝗮𝘁𝗲 𝗶𝗺𝗺𝘂𝗻𝗶𝘁𝘆: the body’s 𝘳𝘢𝘱𝘪𝘥-𝘳𝘦𝘴𝘱𝘰𝘯𝘴𝘦 team 

  • Acts within hours 
  •  Relies on germline encoded receptors (𝘱𝘢𝘵𝘵𝘦𝘳𝘯 𝘳𝘦𝘤𝘰𝘨𝘯𝘪𝘵𝘪𝘰𝘯 𝘳𝘦𝘤𝘦𝘱𝘵𝘰𝘳𝘴 𝘗𝘙𝘙s) to detect pathogens or tissue damage [1]. 
  • Cells involved: neutrophils, macrophages, DC, NK cells, and innate lymphoid cells (ILCs) 
  • Fast, consistent, and non-specific, considered ´memory-less´ [2]. 

𝗔𝗱𝗮𝗽𝘁𝗶𝘃𝗲 𝗶𝗺𝗺𝘂𝗻𝗶𝘁𝘆: the specialized memory force 

  • Takes days to mobilize, but brings precision and memory 
  • Relies on 𝘴𝘰𝘮𝘢𝘵𝘪𝘤𝘢𝘭𝘭𝘺 𝘳𝘦𝘢𝘳𝘳𝘢𝘯𝘨𝘦𝘥 𝘳𝘦𝘤𝘦𝘱𝘵𝘰𝘳𝘴 (TCRs and BCRs) to recognize specific antigens [1]. 
  • Cells involved: B and T lymphocytes, which differentiate into effectors and long-lived memory cells 
  • Remembers past encounters, mounting faster and stronger responses upon re-exposure [2]. 

𝗠𝗲𝘁𝗮𝗽𝗵𝗼𝗿 𝘁𝗼 𝗿𝗲𝗺𝗲𝗺𝗯𝗲𝗿 𝗶𝘁 𝗯𝘆: 

Innate immunity is like prison guards — always on, reacting immediately, preventing prisoners from escape. 
Adaptive immunity is like special forces — slower to act, but trained and remembered for life. 

𝗕𝗹𝘂𝗿𝗿𝗶𝗻𝗴 𝘁𝗵𝗲 𝗯𝗼𝘂𝗻𝗱𝗮𝗿𝗶𝗲𝘀 
Recent research shows the line between innate and adaptive immunity isn’t absolute: 

  • Innate-like lymphocytes (𝗡𝗞𝗧 𝗰𝗲𝗹𝗹𝘀, γδ 𝗧 𝗰𝗲𝗹𝗹𝘀, 𝗠𝗔𝗜𝗧 𝗰𝗲𝗹𝗹𝘀) exhibit features of both types 
  • 𝘛𝘳𝘢𝘪𝘯𝘦𝘥 𝘪𝘮𝘮𝘶𝘯𝘪𝘵𝘺, as described by Netea and colleagues, demonstrates that innate cells can acquire memory-like properties 𝘷𝘪𝘢 𝘦𝘱𝘪𝘨𝘦𝘯𝘦𝘵𝘪𝘤 𝘳𝘦𝘱𝘳𝘰𝘨𝘳𝘢𝘮𝘮𝘪𝘯𝘨, 𝘢𝘭𝘭𝘰𝘸𝘪𝘯𝘨 𝘮𝘢𝘤𝘳𝘰𝘱𝘩𝘢𝘨𝘦𝘴 𝘰𝘳 𝘕𝘒 𝘤𝘦𝘭𝘭𝘴 𝘵𝘰 𝘳𝘦𝘴𝘱𝘰𝘯𝘥 𝘳𝘰𝘣𝘶𝘴𝘵𝘭𝘺 𝘵𝘰 𝘴𝘦𝘤𝘰𝘯𝘥𝘢𝘳𝘺 𝘪𝘯𝘴𝘶𝘭𝘵𝘴 [3]. 

𝗥𝗲𝗮𝗹-𝗹𝗶𝗳𝗲 𝗶𝗹𝗹𝘂𝘀𝘁𝗿𝗮𝘁𝗶𝗼𝗻 
I scraped my knee: Neutrophils arrive to site within hours (innate), clearing pathogens. Days later, T and B cells arrive (adaptive), generating long-term memory. In some individuals, innate mechanisms may be ´trained´ by previous exposures [3]. 

𝗧𝗮𝗸𝗲𝗮𝘄𝗮𝘆 
Innate immunity is fast but forgetful. Adaptive immunity is slow but unforgettable. T𝘩𝘪𝘴 𝘴𝘺𝘴𝘵𝘦𝘮 𝘪𝘴 𝘮𝘰𝘳𝘦 𝘧𝘭𝘦𝘹𝘪𝘣𝘭𝘦 𝘢𝘯𝘥 𝘪𝘯𝘵𝘦𝘳𝘤𝘰𝘯𝘯𝘦𝘤𝘵𝘦𝘥 𝘵𝘩𝘢𝘯 𝘵𝘦𝘹𝘵𝘣𝘰𝘰𝘬𝘴 𝘰𝘧𝘵𝘦𝘯 𝘴𝘶𝘨𝘨𝘦𝘴𝘵 [1–3]. 

Stay tuned for 𝗗𝗮𝘆 𝟰: 𝗛𝗲𝗺𝗮𝘁𝗼𝗽𝗼𝗶𝗲𝘀𝗶𝘀 – 𝘄𝗵𝗲𝗿𝗲 𝗶𝗺𝗺𝘂𝗻𝗲 𝗰𝗲𝗹𝗹𝘀 𝗰𝗼𝗺𝗲 𝗳𝗿𝗼𝗺 

References 
1. Janeway’s Immunobiology 
2. DOI: 10.1038/nri.2015.3 
3. DOI: 10.1126/science.aaf1098 

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