MBTPS1 and viral infectious disease: To confirm that the increase in STAT-1 mRNA and protein levels reflects an increase in a functional interferon system, we challenged control and MBTPS1 KO HT-29 cells with polyinosinic:polycytidylic acid (Poly(I:C)), an immune-stimulant that mimics viral infection (41), and measured the levels of CXCL1, one of the chemokines generated in response to this type of challenge.