TLR4 and necrotizing enterocolitis: Interestingly, the macrophage infiltration we detected in the anemic intestine remained intact in anemic TLR4−/− mice and in anemic mice that carried few native Gammaproteobacteria and did not receive Serratia. Although Gram-negative bacteria can be recognized via pathogen recognition receptors other than TLR4 and may still play a role, these findings are of interest in light of emerging data on enteric dysbiosis in NEC pathogenesis30, and call for investigation to ascertain if these microbial communities also play a role in the subgroup of infants who develop NEC following transfusions.