Functional mushrooms are considered "immune modulators", meaning they can help to calm an overactive immune system, unlike "immune boosters", which simply work to enhance the immune response. Some research has shown that the polysaccharide metabolites in medicinal mushrooms have immunoregulatory properties and, therefore, could help in the treatment of autoimmune disorders by helping to restore a healthy immune system (1)(2).
However, whether or not medicinal mushroom extracts are autoimmune protocol compliant still remains a grey area, as more research is needed to confirm the connection between functional mushrooms and autoimmune conditions.
Referenced sources:
Lull, C, Wichers, H, et al (2005). Antiinflammatory and Immunomodulating Properties of Fungal Metabolites.
Shuang, Z, Gao, Q (2020). Immunomodulatory Effects of Edible and Medicinal Mushrooms and Their Bioactive Immunoregulatory Products.