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Nepene t1_j3qtqa0 wrote

The body makes immunity by having immune cells like B cells which produce antibodies. Those lock onto the antigens of microorganisms that invade your body. There's a lot of complexity beyond that, but generally the limit is whether the microorganism has an antigen that fits an antibody your body has.

If it's fairly close, the body can use a partial fit to make more similar antibodies, so it doesn't need to be a perfect fit.

There's no hard limit that we could reach in a lifetime. Thanks to V(D)J recombination and Somatic hypermutation, there's a very high variance in possible combinations. It's just a matter of if you are lucky enough to have the right antibodies.

However, if you are repeatedly infected by something, it can occupy a large amount of your immune memory e.g. how most T cells in the elderly might be fighting HCMV antigens so it's complicated. Research is ongoing as to the limits of each factor.

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djublonskopf t1_j3t04n9 wrote

Mounting any one immune response also requires a significant amount of energy...in studies on mice, older mice mounting an antibody response to an injected antigen aren't fully able to maintain their body temperature at the same time. So while I don't have hard numbers for humans, if you were taking dozens or hundreds of different vaccines in a short time you'd probably hit a point where the metabolic load was too much for the rest of the body....

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