IFNL1 and tropical spastic paraparesis: Thus, it is possible to infer that IFN-λ3 and two other interferons, IL-28A and IL-29, can activate the JAK-STAT cascade, which is similar and probably synergistic with type 1 interferons (e.g., interferon alpha), although using different receptors, and contributing to the immune pathogenesis of HAM/TSP.