Table I.

Putative interplay between microbes, the alloimmune response and the allograft fate.

Type of Microbe	Immune Consequence	Postulated Effect on Allograft
Resident commensals	Induced local Tregs	Prevents local and/or distal rejection ? OR reduces protective anti-microbial immunity resulting in infections promoting alloreactivity?
Resident commensals	Induced local T effectors	Promotes local and/or distal rejection? OR promotes protective anti-microbial immunity to prevent infections from driving rejection?
Resident commensals	Bacterial products traveling systemically poise APC to present antigen (alloantigen?)	Promotes distal rejection? OR promotes protective anti-microbial immunity to prevent infections from driving rejection?
Acute intestinal infection	Breach in barrier integrity can result in development of T and B cell memory to commensal antigens	Potential cross reactivity of these memory lymphocytes with alloantigens and resistance to immunosuppression => promotes rejection?
Acute infection	PRR activation and inflammatory cytokines can enhance alloantigen presentation and determine T cell differentiation	Promotes local (?) and distal rejection