In the fetal stage, LTi cells will entry the lymph nodes or Peyer’s patches anlagen through the interaction between integrin α4β7 and MAdCAM-1 on the HEVs. CXCL13 secreted by LTo cells will also help to recruit LTi cells through interact with CXCR5 on them. Then LTi cells start to express lymphotoxin α1β2 (LTα1β2) and engage with the stromal cells expressing its receptor LTβR. This interaction will stimulate the stromal cells to upregulate TRANCE, CXCL13, CCL19, CCL21, MAdCAM-1, VCAM-1, and ICAM-1, which feedback on LTi cells to enhance its LTα1β2 expression and recruit more LTi as well as T and B cells in to the anlagen site.