That's describing immunofluorescence microscopy, a more labor-intensive way of doing it. I assume ELISA is more widely used nowadays. And they do mention the option of using human cell lines - that would be the better choice as you want to see if there are antibodies against human nuclear proteins/antigens. Animal cells will have homologous proteins/antigens which some of the antibodies would likely still recognize, but human ones would be better. In an ELISA you would just use purified human proteins/antigens.