Lymphotoxins from distinct types of lymphoid cells differentially contribute to neuroinflammation.

Lymphotoxin α and lymphotoxin β (LTs), TNF superfamily members, are expressed in either soluble (LTα 3 ) or membrane-bound (LTα 1 β 2 or LTα 2 β 1 ) forms. In the pathological context, LT-mediated signaling is known to exacerbate autoimmunity by perpetuating inflammation and promoting the formation of tertiary lymphoid organs. Despite this understanding, the exact roles of LTα and LTβ in the pathogenesis of the murine model of multiple sclerosis, and experimental autoimmune encephalomyelitis (EAE), remain controversial. Here, we employed a panel of gene-modified mice with cell-type restricted ablation of LTα (targeting both membrane-bound and soluble forms of LTs) to unravel the contributions of LTs from various lymphoid cells, namely T cells, type 3 innate lymphoid cells (ILC3) and B cells, in EAE. We found that the effects of LTα deletion were dependent on the cellular source. ILC3-derived lymphotoxins exerted a protective role in EAE by regulating the accumulation of IFN-ɣ- and GM-CSF-producing T H cells in the CNS. In contrast, T-cell-derived lymphotoxins promoted IL-17A- and GM-CSF-mediated T H responses in the periphery, whereas B-cell-derived lymphotoxins were pathogenic only in the autoantibody-mediated EAE model. Collectively, our findings unveil the multifaceted involvement of lymphotoxins in EAE pathogenesis and challenge the view that lymphotoxins play a solely pathogenic role in neuroinflammation.