Anti-C1 antibodies are used in antigen-specific immunodetection in biological samples. The target C1 is a known alias name of the protein Rho GTPase activating protein 4, encoded by the ARHGAP4 gene in humans. This 946-amino acid residue protein is known to be involved in cytoskeleton organization and the regulation of cell migration, among other biological processes. It is localized to the cytoplasm of the cell. It is reported to be expressed in the seminal vesicle, lymph node, lung, bone marrow, and appendix.