The interplay between the antiphospholipid syndrome and systemic lupus erythematosus.

Antiphospholipid syndrome (APS) was firstly described in systemic lupus erythematosus (SLE), but it was recognized also as a primary APS (PAPS) form. These forms are not always distinguishable, since they show some common clinical/serological manifestations. We actually may deal with: (1) patients initially classified as PAPS gradually developing SLE; (2) patients with SLE and associated APS, whose complications generally affect morbidity and mortality; (3) patients with SLE and positive antiphospholipid antibodies without APS manifestations; the relevant issue in such patients is to provide effective prophylaxis. The close relationship between PAPS and SLE is also supported by: (i) nuclear autoimmunity and (ii) complement activation at least in animal models of APS. Future studies on the genetic background and/or on regulatory suppressive mechanisms may clarify how and why PAPS can evolve into SLE.