Caffeine is one of the most widely used neurostimulants in the world and there is considerable debate on its effect in immune cells. One of its main targets is proposed to be adenosine receptors which mediate an anti-inflammatory switch in activated immune cells while another target is phosphodiesterase where it acts as an inhibitor. In macrophages, caffeine has been shown to cause both pro-inflammatory (M1) and anti-inflammatory (M2) phenotypes. If the primary effect of caffeine on macrophages were to antagonize adenosine receptors we would expect cells exposed to caffeine to have a prolonged M1 response. However, we show that caffeine suppresses phagocytosis at physiological concentrations (an indicator of M2 phenotype). This suppression was reversed when macrophages were pretreated with protein kinase A inhibitor, suggesting that at physiological concentrations caffeine's phagocytic suppression may be due to its function as a phosphodiesterase inhibitor, pushing cells towards an M2 fate. However, mRNA expression profiling suggests that caffeine can modulate A2A receptor expression and suppress MKP-1 expression, a hallmark of M1 macrophages. Caffeine is, therefore an immunomodulator that can suppress or prolong inflammatory responses in macrophages, which may account for the abundance of contradicting evidence in the literature. Additionally, these effects are complicated by regular caffeine intake and fitness level, emphasizing that tolerance and immune robustness are important factors in macrophage activation.



College and Department

Life Sciences; Microbiology and Molecular Biology



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caffeine, macrophage, phagocytosis, adenosine receptors, inflammation

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Microbiology Commons