Differential tetraspanin expression in monocyte subsets may regulate the formation of multinucleated giant cells

• Main Author: Champion, Thomas
• Other Authors: Monk, Pete ; Partridge, Lynda ; Wong, Siew Cheng
• Published: University of Sheffield 2016
• Subjects: 610
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.700889

Monocytes are able to undergo homotypic fusion to produce different types of multinucleated giant cells in response to infection (Langhans giant cells in tuberculosis) or rejection of foreign bodies (foreign body giant cells on medical implants). Monocytes exist as a heterogeneous population consisting of three subsets: ~85% classical, ~5% intermediate and ~10% nonclassical at steady state. However, during tuberculosis, the circulating populations of intermediate and nonclassical monocytes increase, suggesting they may play a role in the disease outcome. Monocyte fusion is a highly coordinated and complex process requiring the upregulation and expression of multiple proteins to carry out fusion. Tetraspanins are a family of membrane proteins that associate with partner proteins and other tetraspanins to form a tetraspanin enriched microdomain. Tetraspanins have been shown to associate with fusion proteins and it has been suggested that they play a role in coordinating homotypic monocyte fusion. In this study, peripheral human monocytes were purified by FACS into classical (CD14++CD16-), intermediate (CD14++CD16+) and non-classical (CD14+CD16++) monocytes. Monocyte subsets were induced to fuse using concanavalin A (ConA) and we showed the intermediate monocytes were able to fuse faster and form significantly larger giant cell types. Furthermore, when antibodies targeting CD9, CD53, CD63 and CD151 were added, only the intermediate monocytes showed any inhibition of fusion. A flow cytometry panel was used to report on the expression of 7 tetraspanins (CD9, CD37, CD53, CD63, CD81, CD82 & CD151) on the surface of monocytes before and after addition of ConA. We found that freshly isolated intermediate monocytes are particularly tetraspanin abundant. After 4hrs of culture in ConA, the subsets all show a significantly decreased expression of CD37, CD53 and CD82. We also identified a small population of CD9High Cl that also expressed higher levels of CD63, CD81 and CD151 compared to CD9Low. However, the CD9High Cl did not show any greater potential to fuse and its role in immunity remains unknown.