[Systemic lupus erythematosus and lymphopenia: Clinical and pathophysiological features]

Lymphopenia is frequent in systemic lupus erythematosus (SLE) and profound (<500/mm³) in 10% of cases. T lymphocytes, especially CD4+, are more affected than B cells. The pathophysiological mechanisms are complex, involving lymphocytotoxic antibodies, excess of apoptosis, increased susceptibility of T cells to complement mediated cytolysis, as well as lymphopoiesis impairment and lymphocyte sequestration. Lymphopenia in SLE is independent from other cytopenia and immunosuppressive drug regiments, and associated with disease activity, risk of flare and damage scores. Infectious risk is mostly bacterial, and lymphopenia <1 G/L is an independent risk factor for severe bacterial infections occurrence. The T cellular deficiency is associated with less control of viral replication, but severe and symptomatic infections are scarce. Although exceptional in SLE, pneumocystis is more severe than in HIV+ patients, and risk of progressive multifocal leukoencephalopathy seems increased compared to other rheumatic diseases. To date, there are no specific recommendations for management of SLE with lymphopenia. Infectious prophylaxis should remain exceptional and discussed on a case by case basis. Further studies are needed to assess the clinical characteristics and outcomes of patients with SLE and profound lymphopenia (<500/mm³), which are probably a subset of SLE with primary immunodeficiency and require specific management.