Although generally immunosuppressive as a result of TH1 and other pro-inflammatory cytokine depression (Béguelin et al., 2015) and the promotion of Treg survival and immunosuppressive activity (Stirm et al., 2021), IL-10 activates Janus kinase (JAK)-signal transducer and activator of transcription (STAT) (JAK-STAT) signalling in B-cells (Gupta et al., 2012; Béguelin et al., 2015; Stirm et al., 2021), promoting their proliferation and survival. Here, IL10 is linked to major depressive disorder.