Ectopic LTαβ Directs Lymphoid Organ Neogenesis with Concomitant Expression of Peripheral Node Addressin and a HEV-restricted Sulfotransferase

Lymph node (LN) function depends on T and B cell compartmentalization, antigen presenting cells, and high endothelial venules (HEVs) expressing mucosal addressin cell adhesion molecule (MAdCAM-1) and peripheral node addressin (PNAd), ligands for naive cell entrance into LNs. Luminal PNAd expression requires a HEV-restricted sulfotransferase (HEC-6ST). To investigate LTαβ's activities in lymphoid organogenesis, mice simultaneously expressing LTα and LTβ under rat insulin promoter II (RIP) control were compared with RIPLTα mice in a model of lymphoid neogenesis and with LTβ^−/− mice. RIPLTαβ pancreata exhibited massive intra-islet mononuclear infiltrates that differed from the more sparse peri-islet cell accumulations in RIPLTα pancreata: separation into T and B cell areas was more distinct with prominent FDC networks, expression of lymphoid chemokines (CCL21, CCL19, and CXCL13) was more intense, and L-selectin⁺ cells were more frequent. In contrast to the predominant abluminal PNAd pattern of HEV in LTβ^−/− MLN and RIPLTα pancreatic infiltrates, PNAd was expressed at the luminal and abluminal aspects of HEV in wild-type LN and in RIPLTαβ pancreata, coincident with HEC-6ST. These data highlight distinct roles of LTα and LTαβ in lymphoid organogenesis supporting the notion that HEC-6ST–dependent luminal PNAd is under regulation by LTαβ.