GVHD pathophysiology phase 1: transplant conditioning and inflammation. Following conditioning (radiation and/or chemotherapy), the integrity of the GI mucosa becomes compromised allowing the release of DAMPS and PAMPS, which in turn promote the production of proinflammatory cytokines from recipient cells. These cytokines contribute to host APC (hematopoietic and nonhematopoietic) activation in the gut and lymphoid tissue. GVHD impacts on the gut microbiota, reducing its diversity with a loss of enteric commensal organisms and an outgrowth of pathogenic microbes that further exacerbates the pathological DAMP/PAMP cascade.