The relationship between dysbiosis and MDD has been hypothesized to involve the microbiota-inflammasome-brain connection, whereby dysbiosis caused by stress and GI conditions exacerbates MDD via upregulation of pro-inflammatory pathways including the caspase-1-dependent, pro-inflammatory NLRP3 inflammasome present in several immune cell types (e.g., microglia, monocytes, granulocytes, T cells, B cells) (51). This evidence concerns the gene NLRP3 and major depressive disorder.