C4A and Huntington disease: Given the multiple observations of a potential mode of HD toxicity via nuclear processes, including a more aggressive disease phenotype when an Httex1 transgene was directly fused to a nuclear localization signal (NLS; Davies et al., 1997; DiFiglia et al., 1997; Steffan et al., 2000; Benn et al., 2005, 2008; Atwal et al., 2007), we now show that C4 scFv is primarily cytoplasmic when compared with VL12.3 over a range of assay systems, and confirm C4 scFv cytoplasmic localization in brain cells by confocal microscopy.