We are looking at human-porcine chimeras, and are using anti-human nuclear antigen to stain human cells in these chimeras. Surprisingly, our HuNu stains positive for cytoplasm, and there was no nuclear staining. This antibody is specific for human cells and not for porcine cells. We have used human cells and porcine cells as controls, and both produced desired results with this antibody i.e., positive and negative staining, respectively. I am looking for possible explanations for cytoplasmic staining in our chimeras.