Systemic lupus erythematosus and infections: clinical importance of conventional and upcoming biomarkers.

Infection is a common problem and has become one of the leading causes of morbidity and mortality in patients with systemic lupus erythematosus (SLE). The reasons for the high incidence of infection are immunosuppressive therapy and immune disturbances of lupus itself. Infections may mimic exacerbations of SLE, leading to confusion over the diagnosis and appropriate treatment. It can be notoriously difficult to differentiate between infection and disease flare in some cases. Indeed they may co-exist. Along with the conventional biomarkers of lupus flares as hypocomplementemia, anti-double-stranded-DNA antibodies and erythrocyte sedimentation rate, other biomarkers as procalcitonin, and autoantibodies against complement fraction C1q, have been investigated to distinguish infections from other inflammatory processes. Recent research has provided data about new potential biomarkers to assist clinical decision-making in the management of SLE patients (e.g. percentage of circulating CD27 high plasma cells from the peripheral blood, 2'5'-oligoadenylate synthetase isoforms, soluble triggering receptor expressed on myeloid cells-1 and pentraxin 3), but only some of them are supported by convincing evidence, such as CD 64-Fc receptor expression. We reviewed the literature on the available tests to discriminate between SLE activity and infections, focusing on conventional and upcoming biomarkers.