Chaga mushrooms have become quite popular over the last couple of years. They’re mostly known for their antioxidants and their supposed immune boosting properties. Whilst there is some evidence to suggest that they can improve immune systems, a lot of the claims from supplement manufacturers are a little overblown to say the least.
Nutritional Composition of Chaga Mushrooms
The exact nutritional composition of chaga mushrooms are not exactly well defined. However in general the studies we have to work with do regularly show that they are rich in antioxidants, triterpenoids, melanins, polysaccharides, polyphenols, and flavans.  The problem is that they’re wildly inconsistent. Meaning that ultimately most of the mushroom itself is waste product when it comes to the potential health benefits.
Antioxidant Properties of Chaga Mushrooms
Starting with one of the reasons that chaga mushrooms are believed to boost immunity is the high antioxidant content. Antioxidants help prevent cell damage caused by free radicals or oxidants. 
Oxidative stress occurs when the body cannot produce enough antioxidants. This can in turn then contribute to the development of various health conditions and the aging process in general. By consuming chaga mushrooms, individuals may increase their antioxidant intake and reduce oxidative stress, thereby supporting immune function.
Chaga Mushrooms, Cytokines and Immune Function
Cytokines which are the body’s chemical messengers. Which means they play a vital role in stimulating white blood cells. And these cells are of course the immune system's first line of defense.
Quite a few studies have found that chaga mushrooms may help regulate the production of cytokines thereby enhancing immune function. 
By promoting more effective communication between immune cells, chaga mushrooms may assist in fighting infections and strengthening the immune response.
Chaga Mushrooms and Inflammation
Chronic inflammation can lead to various health problems. And Chaga mushrooms have been shown to regulate inflammatory cytokine production as well as those that are a part of the immune system directly.
The Problem With Chaga Mushrooms
The main issue with Chaga is the same issue that most mushroom supplements have. And that is that most of the content is waste product, which in turn makes dosage very difficult to determine.
Some studies on commercially available products showed that almost all had less than 20% of the useful compounds. 
Other Potential Benefits of Chaga Mushrooms
There are a couple of other supposed although less well researched effects:
1. Lowering Cholesterol Levels
There have been a few animal studies that have shown chaga mushrooms may help lower "bad" cholesterol levels. This cholesterol is what is referred to as LDL cholesterol. And of course high levels of LDL cholesterol are associated with a lot of negative health implications.
2. Reducing Blood Pressure
There is also some early research that suggests chaga mushrooms may have a blood pressure lowering effect.
Animal studies have shown that chaga extract could potentially reduce high blood pressure. However a lot of things that work in animals don’t translate over to human studies. As such human trials needed to confirm these findings and determine the appropriate dosage for blood pressure management.
So, Is Chaga Good For Immunity?
All in all we'd say there's decent evidence to suggest Chaga is in fact good for immunity. The only issue we have is that the content of Chaga mushrooms is wildly varied and there is generally a lack of standardized extracts.
1 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8124789/
2 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9268247/
3 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3774877/
4 - https://www.ncbi.nlm.nih.gov/books/NBK92757/table/ch9-t1/