Caffeine affects the immune system via at least two opposing mechanisms.

Mechanism 1: A2A receptor antagonism (immunostimulatory) Tumors and damaged tissues release adenosine, which engages the A2A receptor on immune cells and signals them to stand down. Caffeine antagonizes (i.e., blocks) this receptor.

Mechanism 2: Raising intracellular cAMP (immunosuppressive) Caffeine also inhibits phosphodiesterase, the enzyme that hydrolyzes (i.e., breaks down) cAMP. cAMP accumulates inside immune cells, which acts as a "calm down" signal.

Note: both mechanisms are dose-dependent. At dietary caffeine levels, A2A antagonism likely dominates, whereas PDE inhibition is weak and mainly relevant at higher concentrations. However, the net immune effect in the tumor microenvironment remains unproven.

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If you would like to learn more, I can outline a framework for technical folks to ease in and become more informed on cancer. Gaps abound. The more people who understand cancer, the faster we get to cures. Moreover, personalized cancer treatment is the obvious future. Knowledge acquired now may pay off later (but hopefully not needed).

All you haters that give me grief for drinking my daily cup of decaf can shut up now.

https://www.mdpi.com/2072-6643/18/6/877

I didn’t dig in too deeply, but started drinking a morning cup of sugar free double mocha cappuccino, to help my workouts.

If I’m fooling myself, don’t tell me. I like the cappuccino.