Table 1.

Examples of changes in host physiology resulting in changes in the gut microbiota

Component	Function	Findings	Ref
MUC2	Physical barrier	MUC2 deficient mice have bacteria in direct contact with the mucosa leading to inflammation	48
RegIIIγ	Antimicrobial activity	Reduced expression results in the expansion of opportunistic Gram-positive pathogens	62
IgA	Antimicrobial activity	Commensal specific IgG develops in absence of IgA expression	90
MyD88	Microbial detection	MyD88−/− mice have commensal bacteria in liver and spleen	77
NOD2	Microbial detection	NOD2−/− mice have reduced bactericidal activity and an expansion in mucosal microbial colonization	70
MHC	Antigen presentation	Bacterial composition and activity varies according to MHC haplotype	87

MUC, mucin; Ig, immunoglobulin; NOD, nucleotide-binding oligomerization domain; MHC, major histocompatibility complex.