The Science & Significance of Trained Immunity

ISSUE N.2

The Science & Significance of Trained Immunity

Right away, I found myself asking another question. If innate immune cells don't make antibodies or memory cells, what would memory look like?

One year after the 2011 concept paper I shared last week, Jessica Quintin and colleagues published one of the first studies that began testing the idea experimentally. It's also the paper where beta-1,3/1,6-glucan first enters this story.

The researchers designed something simple – they used mice bred to have no functioning adaptive immune system at all.

No mature T cells, no mature B cells and no antibodies.

Based on everything we understood at the time, these mice shouldn't have been capable of immune memory of any kind.

The mice were exposed once to a low dose of Candida albicans, allowed to recover, then challenged again later with what should have been a lethal reinfection.

They survived at dramatically higher rates than mice with no prior exposure.

Then the researchers depleted the mice's monocytes specifically, and the protection disappeared.

The protection wasn't coming from the adaptive immune system. Something about the innate immune response had changed after that first encounter.

The study didn't show that innate immunity works the way adaptive immunity does. It showed something more interesting: innate immune cells could be functionally changed by a previous exposure, enough to respond differently the next time.

One more finding, and I'll leave it right here for now: the researchers also showed that purified beta-1,3/1,6-glucan – a structural molecule from the fungal cell wall – was enough on its own to train human monocytes in the lab. The whole organism wasn't required. One naturally occurring signal was enough to start the process.

This study made trained immunity real for me. Not because I suddenly understood every mechanism behind it — I didn't, and I still don't fully — but I am learning! It was because memory outside the adaptive immune system landed conceptually.

That shifted the question I was asking. It stopped being "Can the innate immune system learn?" and became "why and how does it learn?" I'm still working through that one.

Clinically, it deepens the reframe from last week, now with real data behind it: instead of thinking in terms of boosting or suppressing, we can start asking whether trained immunity may be part of the patient's story, and how that is significant. Hint: it has the readiness and coordination to respond better to whatever comes next.

It's also part of why beta-1,3/1,6-glucan has become such an important molecule in this research – not because it's another immune-support ingredient, but because it was one of the first naturally occurring signals shown to initiate this kind of functional change.

Next week, I want to sit with the question this naturally raises: how does an immune cell recognize what is worth responding to?

Reference
Quintin J, Saeed S, Martens JHA, et al. Candida albicans infection affords protection against reinfection via functional reprogramming of monocytes. Cell Host & Microbe. 2012;12(2):223-232. doi:10.1016/j.chom.2012.06.006. PMID: 22901542.