Memory B cells (MemB), along with long-lived plasma cells, are a cornerstone of humoral immune memory, supporting prolonged immune defense following infection or vaccination. Recent investigation into the influence of epigenetics on cell fate and identity maintenance have spurred investigations into the role of epigenetic modifications in immune memory formation, heralding the pursuit of epigenetic memory as a central avenue of research.

On March 29, a research team led by Profs. HOU Baidong and ZHU Bing from the Institute of Biophysics of the Chinese Academy of Sciences unveiled a distinctive facet of the epigenetic makeup of antiviral MemB.

Their findings, which highlight the intertwined properties of adaptive and innate immune memory in antiviral MemB, were reported in a paper published in Science Advances.

Using phage Qβ-derived virus-like particles (Qβ-VLP) as a model antigen in mice, the researchers observed a remarkable phenomenon during the memory recall response: increased transcription of a subset of innate immune response genes in MemB. This increase in transcription, akin to a form of innate immune memory or "trained immunity," coincided with increased chromatin accessibility in resting MemB, suggesting that pre-existing epigenetic changes prime these genes for a robust response to signaling cues.

In addition, the researchers found that the innate immune memory phenomenon was exclusive to antiviral MemB, as MemB induced by soluble protein antigens did not show increased transcription of these genes. The authors speculate that this innate immune memory in antiviral MemB may serve as a shield against reinfection when the virus is encountered again.

Given the antiquity of innate immunity in evolutionary terms, the adaptive immune system retains vestiges of innate immune cell memory mechanisms that reflect biological adaptation to environmental challenges.

This study reveals the integration of innate immune memory, encoded in epigenetic cues, with adaptive immune memory in the domain of antiviral MemB, providing insight into the mechanisms underlying long-term immune memory.

Epigenetic alterations predispose Qβ⁺ MemB to enhanced transcription of anti-viral genes upon antigen re-challenge. (Image by HOU Baidong's group)