Salivary IgA as biomarker of disease activity in Systemic Lupus Erythematosus

Immunoglobulin A (IgA) is the main antibody isotype present in the body fluids such as tears, intestinal mucous, colostrum and saliva. There are two subtypes of IgA in humans: IgA1 mainly present in blood and IgA2, the preferentially expressed mucosal antibody. In clinical practice, immunoglobulins are typically measured in venous or capillary blood; however, alternative samples including saliva are now being considered given its non-invasive and easy collection nature. Since IgA deficiency could be frequently detected in patients with autoimmune diseases, we decided to evaluate the levels of both IgA subtypes in serum and saliva of systemic lupus erythematosus (SLE) patients. Specific IgA1 and IgA2 levels were measured by a light chain capture-based ELISA in a cohort of 32 patients with SLE that were compared with antibody levels of healthy volunteers. Surprisingly, our results indicated that in saliva of SLE patients, both IgA subtypes were significantly elevated; however, serum IgA1 levels were decreased when compared with control subjects. Interestingly, we also found that salivary IgA levels, most specifically IgA1, positively correlate with the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) values as well with the amount of serum anti-nucleosomes and anti-dsDNA IgG autoantibodies. Strikingly, we also were able to detect the presence of salivary anti-nucleosome IgA antibodies in SLE patients, a feature that was not previously reported elsewhere. According to our results, IgA characterization in saliva could be used as a pre-diagnostic or follow-up clinical tool in SLE with easier, faster and safer to manipulate than blood samples.