Type III interferons (IFNs) are one of the core IFNs that directly inhibit viral replication, and their function specifically acts on mucosal epithelial cells and certain immune cells. We recently showed that additional human, but not mouse, immune cell types express IFNLR1 mRNA (including T cells) and respond to IFN-λ3 stimulation. T cells are critical members of our adaptive immune system, where CD4+ T cells promote the effector functions of other immune cells, and CD8+ T cells directly kill altered cells. CD4+ T cells can differentiate into distinct T helper (Th) subtypes. We previously showed IFN-λ3 inhibited Th2 cytokine induction in influenza vaccine-stimulated peripheral blood mononuclear cells (PBMCs), but the inhibitory mechanisms were unknown. Since Th2 cytokines are associated with allergic diseases and inflammation, such as Th2-endotype allergic asthma, a better understanding of the interplay between type III IFNs and T cell polarization could aid in the development of future therapies. Little is known about the levels of IFN-λR1 on CD8+ T cells and how CD8+ T cells respond to IFN-λs with or without the presence of T cell receptor (TCR) stimulation. To reveal the distribution of IFN-λR1 on T cells, we screened several antibodies and identified a candidate that can specifically and efficiently bind IFN-λR1. Using the newly identified antibody, we detected unique IFN-λR component IFN-λR1 at protein levels on total human CD4+ T cells and CD8+ T cells as well as different subsets. The percentage of CD8+ T cells expressing IFN-λR1 on the surface (about 10%) was higher than CD4+ T cells (about 2%) at the steady state (p < 0.05). The other component of IFN-λR, IL-10RB, was expressed on almost 100% of CD4+ and CD8+ T cells. In the context of TCR stimulation, IFN-λR1 levels on human T cells were significantly increased over 1-3 days within whole PBMC as well as purified CD4+ and CD8+ T cell cultures in vitro. Through testing multiple TCR signalling inhibitors, we identified multiple signalling intermediates that likely contribute to IFN-λR1 upregulation on T cells after TCR stimulation. Lastly, we demonstrated that IFN-λ3 downregulated IL-13 production in whole PBMCs during TCR stimulation and also during longer-term naïve CD4+ T cell Th2 polarization. For CD8+ T cells, using RNA sequencing transcriptome analyses, we showed that without TCR stimulation, IFN-λ3 inhibited protein synthesis and activated antiviral genes. When comparing transcriptome changes after TCR stimulation, with or without IFN-λ3, we found multiple pathways altered upon IFN-λ3 addition with some overlap to when IFN-λ3 was added alone to CD8+ T cells. Overall, this body of work has demonstrated that human T cells can directly respond to IFN-λ3, although the subset of T cell and activation state dramatically alter the magnitude of IFN-λ responsiveness due to the different surface levels of IFN-λR1. This means that although some T cells (e.g. naïve CD4+ T cells) are poor responders at rest, IFN-λ can directly influence Th2 and CD8+ T cell responses during an infection or periods of chronic inflammation that we wouldn’t have expected if we only studied T cells at steady state. Through the greater understanding of IFN-λ immunoregulatory pathways, IFN-λ3 could be an ideal future immunotherapy going beyond just promoting antiviral pathways and instead targeting specific immune cell types, including T cells, with fewer side effects compared to other IFNs.