LTi cells form a distinct lineage in the family of "innate lymphoid cells" (ILCs). ILCs are a heterogeneous collection of lymphocytes that lack antigen specificity (non-T, non-B cells) and potentially produce characteristic cytokines of T cell subsets (Th1, Th2, Th17). Innate lymphoid cells are sessile cells. They do not circulate through the bloodstream and are thus attributable to the local organ tissue where they are also produced when required.
While LTi-cells are mainly developed and function in the fetal stage, LTi-like cells are thought to arise only in adulthood. They are considered a subset of type 3 ILCs (ILC3s) because they express the ILC3 lineage-defining transcription factor RORγt and, like other ILC3s, can produce an ILC3 signature cytokine, IL-22, and initiate protective immune responses against extracellular bacteria. However, LTi/LTi-like cells have a unique gene expression pattern, and they develop from a precursor that is distinct from the precursor of all other ILCs and the precursor of conventional natural killer (cNK) cells. LTi/LTi-like cells play a central role in lymphoid organogenesis (Zhong C et al. 2018). For more, see below. LTi cells.