Differences in susceptibility between C57BL/6 substrains C57BL/6 J and C57BL/6By after intravenous L. monocytogenes inoculation have been linked to differential Ifnb1 expression, with increased IFNβ levels increasing susceptibility to infection, thus emphasizing the potentially important role of cytokine expression in strain susceptibility [132]. The gene discussed is IFNB1; the disease is infection.