The Role of Metalloproteinase ADAM17 in Regulating ICOS Ligand–Mediated Humoral Immune Responses

Abstract

Immune cells regulate cell surface receptor expression during their maturation, activation, and motility. Although many of these receptors are regulated largely at the level of expression, protease-mediated ectodomain shedding represents an alternative means of refashioning the surface of immune cells. Shedding is largely attributed to a family of a disintegrin and metalloprotease domain (ADAM) metalloproteases, including ADAM17. Although ADAM17 is well known to contribute to the innate immune response, mainly by releasing TNF-α, much less is known about whether/how this metalloprotease regulates adaptive immunity. To determine whether ADAM17 contributes to regulating adaptive immune responses, we took advantage of ADAM17 hypomorphic (ADAM17ex/ex) mice, in which ADAM17 expression is reduced by 90–95% compared with wild-type littermates. In this study, we show that that ADAM17 deficiency results in spleen and lymph node enlargement, as well as increased levels of Ag-specific class-switched Ig production following immunization with OVA together with anti-CD40 mAbs and polyinosinic-polycytidylic acid. Moreover, we demonstrate that the costimulatory ligand ICOS ligand (ICOSL) is selectively downregulated on the surface of B cells in an ADAM17-specific manner, although it is not proteolitically processed by recombinant ADAM17 in vitro. Finally, we show that higher cell surface levels of ICOSL in ADAM17ex/ex mice may contribute to the development of excessive Ab responses. Therefore, our data suggest a functional link between ADAM17 and ICOSL in controlling adaptive immune responses.

ADAM10-Mediated ICOS Ligand Shedding on B Cells Is Necessary for Proper T Cell ICOS Regulation and T Follicular Helper Responses

“…Consistent with a previous report(16), treatment of purified WT B cells with PMA resulted in reduced ICOSL shedding in ADAM17 −/− and ADAM10/17 −/− B cells compared to WT (Fig. 2c), confirming a role for ADAM17 in the PMA-stimulated ICOSL shedding.…”

“…Given the above results and a previous report (16) that ADAM17 may be involved in the regulation of ICOSL, we sought to conclusively determine whether ADAM10 and ADAM17 can directly cleave ICOSL. To test this, recombinant mouse (rm) ICOSL was incubated with rmADAM10 or rmADAM17.…”

“…1b). Given that ADAM17 has been reported to be involved in ICOSL shedding (16) we also examined B cells that lacked ADAM17 (ADAM17 B−/− ) as well as B cells from ADAM10/17 B−/− mice. Consistent with previous results, there was no difference in ICOSL levels on ADAM17 −/− B cells compared to WT (Supplemental Fig.…”

“…Defective humoral immune responses in ADAM10 B−/− mice (5, 6) and an earlier report of ADAM17 being important for ICOSL shedding (16) prompted us to examine whether ADAM10 was involved in the shedding of ICOSL. Our studies demonstrate a large increase in ICOSL surface expression on B cells from ADAM10 B−/− mice (Fig.…”

“…There have been several studies illustrating the regulation of ICOS (13–15), particularly at the mRNA level, as well as the cleavage of ICOSL. In particular, ADAM17, was shown to cleave ICOSL in response to Phorbol Myristate Acetate (PMA) and B cell receptor (BCR) crosslinking (16). However, ADAM17 was not involved in ICOS-induced shedding of ICOSL and constitutive ICOSL levels were unchanged.…”