Immune system – non-specific immunological activation by vaccine antigens (NSE)

Immune system – non-specific immunological activation by vaccine antigens refers to the phenomenon of "trained immunity," where certain vaccines provide broad protection against pathogens other than the one specifically targeted by the vaccine (Netea et al., 2020). This process involves the functional reprogramming of innate immune cells, such as monocytes, macrophages, and natural killer cells, through epigenetic modifications and metabolic rewiring (Benn et al., 2013). Unlike the antigen-specific adaptive immune response, these non-specific effects (NSEs) enhance the host's baseline defense mechanisms against a wide array of heterologous infections (Goodridge et al., 2016). Live-attenuated vaccines, including Bacillus Calmette-Guérin (BCG), measles, and oral polio vaccines, are the most prominent examples of agents that trigger this systemic activation. While these effects contribute to significantly reduced all-cause mortality in pediatric populations, the phenomenon represents a complex physiological state rather than a single molecular target like a receptor or enzyme. Consequently, it is studied as a system-level immunological response with significant implications for vaccine design and public health strategies (Aaby et al., 2014).

Other names

Trained immunityNon-specific effects of vaccinesHeterologous immunityInnate immune memoryOff-target vaccine effects

Induction of epigenetic and metabolic reprogramming in innate immune cells, such as monocytes and natural killer cells, leading to increased H3K4me3 histone methylation at the promoters of pro-inflammatory genes and a metabolic shift toward glycolysis, which enhances the host response to unrelated secondary infections (Netea et al., 2016).