Intestinal location- and age-specific variation of intraepithelial T lymphocytes and mucosal microbiota in pigs

Intraepithelial lymphocytes in the pig intestine: T cell and innate lymphoid cell contributions to intestinal barrier immunity

“…Identification of CD2 - γδTCR T cells in the porcine intestine by staining with antibody clone MAC320 [reactive to swine workshop cluster 6 (SWC6) protein expressed by porcine CD2 - γδTCR T cells ( 63 , 64 ); to-date, SWC6 protein has not been fully characterized] demonstrated very few SWC6 + cells (inferred to be CD2 - γδTCR T cells) present, and none were detected in the epithelium ( 65 ). In addition, there are very few CD2 - γδTCR T cells in small or large intestinal epithelium ( 66 , 67 ), confirming CD2 - γδTCR T-IEL absence or rarity throughout the porcine intestine. Therefore, CD2 still remains a potential marker for identifying the majority of IELs in pigs.…”

“…Though measurements of CD2 + and CD3ε + cells are not necessarily equivalent, comparison suggests more preferential localization of lymphocytes to the epithelium of the large compared to small intestine. However, overall IEL abundance is greater in the porcine small than large intestine ( 66 , 67 , 85 – 90 ).…”

“…CD8α + cells are localized preferentially to the epithelium ( 76 , 78 – 81 ), but porcine αβTCR T , γδTCR T, and NK cells can all express CD8α ( 58 ). While NK cells (CD3ε - CD8α + ) are not highly prevalent in the porcine intestinal tract, both γδTCR and CD8 αβTCR T cells occur in the intestine of pigs at regular frequencies ( 62 ), and most γδTCR T-IELs are CD8α + ( 66 , 67 ). Thus, CD8α + IELs mostly includes both γδTCR and αβTCR lineage T cells.…”

“…IEL distributions also vary by locality within crypts and villi and in relation to luminal proximity, including location in the basement membrane, enterocyte nuclear level, or apical epithelium ( Figure 1 ). In porcine small intestine, IELs preferentially congregate to intestinal villi over crypts at up to a four-to-one ratio ( 65 – 67 , 77 , 78 , 83 , 97 , 98 ). Preferential accumulation of IELs in villi suggests IEL effector functions may involve close interactions with signals derived from the intestinal lumen, as villi are more intimately associated with the lumen compared to shielded niches of crypts.…”

“…IELs in small intestinal villi also differ in distribution across the epithelial layer in relation to luminal proximity. While the majority of IELs are located near the basement membrane, some IELs are in closer proximity to the lumen, including at the enterocyte nuclear level, apically, or even freely within the lumen ( 65 , 67 , 78 , 79 , 87 , 97 , 101 ). However, IEL detection within the free lumen must be cautiously interpreted, as technical variables of tissue processing may compromise tissue integrity.…”