Lymph node stromal cells acquire peptide-MHCII complexes from dendritic cells and induce antigen-specific CD4⁺ T cell tolerance.
Bottom Line: Although LNSCs express MHCII, it is unknown whether they can also impact CD4(+) T cell functions.We show that the promoter IV (pIV) of class II transactivator (CIITA), the master regulator of MHCII expression, controls endogenous MHCII expression by LNSCs.Our data reveals a novel, alternative mechanism where LN-resident stromal cells tolerize CD4(+) T cells through the presentation of self-antigens via transferred peptide-MHCII complexes of DC origin.
Affiliation: Department of Pathology and Immunology, University of Geneva Medical School, 1211 Geneva, Switzerland.Show MeSH
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Mentions: We next investigated which cell types are involved in the transfer of MHCII molecules to LNSCs. MHCII-negative LECs and FRCs (Fig. 3 A) were co-cultured for 24 h with MHCII+ cells, namely macrophages, B cells, or LPS-treated DCs. We observed that only DCs were capable of transferring MHCII to LNSCs (Fig. 3 A). In vivo experiments further suggested that this transfer is exclusively mediated by DCs. First, MHCII expression by pIII+IV−/− LNSCs was comparable to pIV−/− LNSCs (Fig. 1 E), demonstrating that B cells, which rely on pIII, are not involved in this process. Second, MHCII expression by LNSCs was not reduced after depletion of macrophages using clodronate liposomes (unpublished data). Only WT and not MHCII−/− DCs transferred MHCII to both WT and MHCII−/− LNSC, ruling out the possibility that DC-derived soluble inflammatory mediators induce endogenous MHCII up-regulation by LNSCs (Fig. 3 B). Furthermore, MHCII transfer from DCs to LECs and FRCs was detectable within 2 h of co-culture and increased over time (Fig. 3 C). Finally, we investigated whether MHCII transfer to LECs and FRCs was different depending on DC activation state. Both untreated DCs (immature DCs [iDCs]) and LPS-treated DCs (mature DCs [mDCs]) transferred MHCII to LNSCs. LNSCs co-cultured with mDC acquired more MHCII compared with those incubated with iDC (Fig. 3 D). Interestingly, DCs cultured for 24 h with LEC/FRC cultures expressed lower MHCII compared with DCs cultured alone (Fig. 3 E), consistent with MHCII transfer from DCs to LNSCs. Importantly, we observed that different ex vivo purified DC subsets from steady-state LN (Fig. S3) transferred MHCII to MHCII-deficient LECs and FRCs (Fig. 3 F), with an efficacy that correlated with the DCs’ own MHCII expression (Fig. S3).
Affiliation: Department of Pathology and Immunology, University of Geneva Medical School, 1211 Geneva, Switzerland.