Searching for host immune-microbiome mechanisms in obsessive-compulsive disorder: A narrative literature review and future directions

•Current literature suggests immune-microbiome signaling could be relevant to OCD.•We discuss mechanisms by which gut-brain-immune axis dysfunction could underlie OCD.•OCD is heterogeneous, and future microbiome investigations should take this into account.•This offers to be a novel area of inquiry to further our understanding and treatment of OCD.