The presence of bacterial flora contributes to the organization of effective microcirculation for the lymph node defence function.

Abstract

For elucidation of microbial effects on rat lymph node microcirculation, intravascular andintralymphatic cast preparations were examined along with histological observation, using light microscopy.Submandibular lymph nodes from conventional (CV), specific-pathogen-free (SPF), antibioticdecontaminated-SPF (AB-SPF) and germfree (GF) rats were studied.In nodes exposed to microbial stimulation (CV and SPF), typical high-endothelial-venules (HEVs) with many lymphocytes within their walls, received abundant vascular connections from the vascularplexuses in the superficial cortex and assumed close proximity to the intermediate sinuses plugged withmany lymphocytes. In nodes with almost no microbial stimulation (AB-SPF and GF), overall vascularitywas sparse, and the vascular connections to the HEVs with few lymphocytes in their walls wereminimal. In the AB-SPF rat nodes, the intermediate sinuses were often vacant, and in the GF ratnodes, they were poorly developed. Arteriovenous anastomoses were frequently observed to join HEVs, regardless of differences in microbial conditions.Therefore, in rat lymph nodes, microbial effects seem to induce a rich blood supply to the HEVsby organizing vascular plexuses in the superficial cortex. This promotes the active traffic of lymphocytesfrom the HEVs into the nodes and formation of intermediate sinuses, and related functions areenhanced.