Methods: LPMs were isolated from normal human jejunum, infected with HCMV, stimulated with TLR4/5 agonists, and assayed for cytokine production. Blood monocytes also were infected with HCMV, but then treated with stroma-conditioned media (S-CM, generated from normal intestinal stroma using our established protocol) to differentiate the monocytes into non-inflammatory macrophages. The S-CM-differentiated macrophages were stimulated with TLR agonists and assayed for cytokines. HCMV infection and replication were determined by confocal and electron microscopy, and RT-PCR.
Results: LPMs infected with HCMV did not support viral replication or produce cytokines, regardless of TLR stimulation. In contrast, blood monocytes, first infected with HCMV and then S-CM differentiated and TLR stimulated, supported replication and produced significantly higher levels of cytokines compared with mock-infected, S-CM-differentiated, TLR-stimulated macrophages.
Conclusions: HCMV non-productively infects LPMs without breaking inflammation anergy. However, when monocytes are infected with HCMV prior to differentiation into intestinal macrophages, inflammation anergy is inhibited. Systemic infection of monocytes by HCMV before recruitment to the mucosa strategically positions pro-inflammatory macrophages to interact with bacteria via TLR4/5, leading to inducible macrophage cytokine responses.