Systemic lupus erythematosus (SLE) is a multisystem, autoimmune disease. It’s characterized by the formation of many different autoantibodies, the most notable of which are antinuclear antibodies. These antibodies are useful for diagnosis, and they also play a big part in the pathogenesis of the disease.

Antinuclear antibodies
Antinuclear antibodies are just what the name implies: antibodies against specific antigens within the cell nucleus. They can be grouped into four categories: 1) anti-DNA antibodies, 2) anti-histone antibodies, 3) antibodies against non-histone proteins bound to RNA, and 4) anti-nucleolar antibodies.

Antinuclear antibodies in general are found in many different autoimmune diseases (like systemic sclerosis and rheumatoid arthritis). Antibodies to double-stranded DNA and a particular antigen called the Smith (Sm) antigen, however, are virtually diagnostic of lupus. Patients with lupus have other, non-antinuclear antibodies too – but here we’re just talking about the antinuclear ones.

How a FANA works
Autoantibodies are usually detected using fluorescent antinuclear antibody (FANA) testing. You can use other methods – like enzyme-linked immunosorbent assay (ELISA) – but immunofluorescent microscopy is the gold standard method. In this method, the lab takes a slide coated with fixed, permeable cells (bought from a manufacturer) and adds some of the patient’s serum to that slide. The serum is allowed to incubate, and is then washed off.

At this point, if the patient has antinuclear antibodies, they will be bound to the slide. You can’t see them, of course, so a second antibody with a fluorescent tag (also bought from a manufacturer) is then applied to the slide, allowed to incubate, and washed off. If the patient has antinuclear antibodies that are bound to the cells on the slide, these antibodies will now fluoresce under the microscope.

This test is cool because you can tell not only if antibodies are present (by seeing green stuff on the cell nuclei) but also what kind of antibodies they might be (by seeing what pattern of positivity is present). Here’s a short summary of different patterns:

• Homogeneous (diffuse) pattern (the whole nucleus stains green – see the above photo): found with antibodies to chromatin, histones, and (occasionally) double stranded DNA. This pattern is seen in lupus and occasionally in other autoimmune diseases.
• Speckled pattern (random speckles all over the nucleus): found with antibodies to non-DNA nuclear antigens (like ribonucleoprotein). This is the most common immunofluorescent pattern overall – and the least specific for any particular autoimmune disease.
• Nucleolar pattern (a few spots of green within the nucleus): found with antibodies to RNA. Found most frequently in patients with systemic sclerosis (a different autoimmune disease)
• Rim or peripheral pattern (green around the periphery of the nucleus): found with antibodies to double-stranded DNA. This pattern is seen frequently in lupus.

What if the FANA is positive?
Most patients with lupus have positive FANA results. So if the FANA is positive, and the patient has symptoms of lupus, then the patient probably has lupus. If the FANA is positive, but the patient does not have symptoms, then it may not be lupus (and you’d just watch closely for signs/symptoms of lupus developing later). FANAs can be positive in people with no autoimmune disease – and the rate of false positivity increases with age. So to make a diagnosis of lupus, you have to use clinical symptoms and the patient’s history along with the FANA results.

Next time we’ll talk about how these antibodies cause problems in lupus.