Paywall, https://www.sciencedirect.com/science/article/abs/pii/S1359610119301479 Sci hub, https://sci-hub.se/10.1016/j.cytogfr.2019.12.008
I wonder if there has been too much focus on the immune system in ME/CFS. As this article says there could be dysfunctional crosstalk between other kinds of cells and with the focus on immune system, that may be why the cause hasn't been found yet. In particular the dysfunctional crosstalk could be between cells that are involved in recovery from exertion. If some of these cells are overreactive, that could lead to the body reacting to minor exertion in perhaps the same way as it would to extreme overexertion.