Downregulation of endogenous zebrafish mpeg1 expression during infection with M. marinum or S. typhimurium has been previously described [16], and our lab has observed severe attenuation of mpeg1 transgene expression in larval macrophages occurring as early as three days post-infection with M. marinum. We describe the development of a new macrophage-specific mfap4 transgenic line that, in contrast to mpeg1, remains stable during mycobacterial infection. The gene discussed is MPEG1; the disease is infection.