And bears poo behind trees.

[Citrusandginger]

Brace yourselves. Scientists from the Karolinska Institutet in Sweden and Imperial College London have shown for the first time which aspects of our immune systems are regulated by sex hormones, and the impacts this has on disease risk and health outcomes in males and females.

Researchers recruited 23 transgender men and collected blood samples from patients before treatment, and then following three months and one year of testosterone treatment, analysing differences in the immune cells and proteins in the blood.

Analysis revealed several key elements of the immune system that changed following treatment, including pathways for inflammatory responses to infections and disease.

To test whether the observed changes were directly due to the increase in testosterone or indirectly from reduced oestrogen, the team analysed blood from 11 female donors. Samples were treated with receptor blockers to show that the effect was directly due to testosterone signalling, rather than loss of oestradiol-signaling.

Sex hormones modulate the immune system to influence disease risk differently | Imperial News | Imperial College London

We performed longitudinal systems-level analyses in 23 trans men and found that testosterone modulates a cross-regulated axis between type-I interferon and tumour necrosis factor. This is mediated by functional attenuation of type-I interferon responses in both plasmacytoid dendritic cells and monocytes. Conversely, testosterone potentiates monocyte responses leading to increased tumour necrosis factor, interleukin-6 and interleukin-15 production and downstream activation of nuclear factor kappa B-regulated genes and potentiation of interferon-γ responses, primarily in natural killer cells. These findings in trans men are corroborated by sex-divergent responses in public datasets and illustrate the dynamic regulation of human immunity by sex hormones, with implications for the health of individuals undergoing hormone therapy and our understanding of sex-divergent immune responses in cisgender individuals.

Immune system adaptation during gender-affirming testosterone treatment | Nature

So the conclusion is that women taking testosterone have immune responses which are more male-like. That's not astonishing, but I don't think it's completely obvious that it would be the case either.

Ok. Not sure this is massive? Are you trying to promote your own research OP?

Umm cross sex hormones are not neutral?

The research in the OP doesn't seem to show anything about males at all, it's all about women and transmen (who are also women). And a teeny weeny dataset.

I don't think anyone thinks they are neutral, OP, if by neutral you think they don't do anything. Obviously testosterone masculinizes the body, and I think trans people are fully aware of this, given this is the whole point of them taking it? This doesn't appear to be a particularly dramatic or negative side effect either, just that you'll likely end up with a more male-type immune system. From conversations with trans man friends I understand they are generally informed that medical risks etc may shift into male rather than female ranges when they start testosterone so this is more confirmation than revelation.

From reading the article, it seems like the intention was not to study trans men specifically but the role of sex hormones in immunity in general, it seems like trans men just happened provided a handy research group to demonstrate the difference is caused by testosterone and not other factors. Though it is good to have some evidence that HCPs shouldn't just default to treating trans people as their birth sex in a medical setting, which is something trans people have been saying for a long time.

Sorry, what was it we were supposed to be "bracing ourselves" for?

Hm, I don't think their research really does what they claim - it may shed some light on differences between men and women but all it can actually show is a difference between women who are and aren't taking testosterone.

Between a tiny unrepresentative sample of women who are taking testosterone for variable short periods of time and a tiny unrepresentative sample of women who aren't taking it at all.

Maybe it establishes a method that could be applied to the study of a larger more representative group, maybe it doesn't.

We need scientific studies, but to be worth anything they need to be large scale (and double blind).

Thanks for posting that Citrus, it was interesting.

It’s about time that someone did some actual research into the health effects of putting exogenous testosterone into female bodies. I’d like to see more of this sort of thing with bigger cohorts, over longer periods of time and with more detailed investigation.

Was this supposed to show that the women taking testosterone had actually changed into men or something?

a bit underwhelming if so…

There's definitely some interesting research to be done on the interaction between hormones and the immune system.

Some came out of Covid research when it was noticed women did better than men - the theory was that oestrogen was a factor, so they tried giving it to men and postmenopausal women to see if that brought their outcomes in line with those of younger women. It did help the former, but did nothing for the latter.

Were the immune changes reversible?