In order to visualize single-cell immune responses, our lab previously used smFISH to monitor the single-cell mRNA expression of two cytokines, IL-1β and TNF-α, in a human monocytic leukemia cell line, THP-1, in response to lipopolysaccharide (LPS), a primary component of cell walls in Gram negative bacteria33. The gene discussed is TNF; the disease is monocytic leukemia.