Altered peripheral lymphocyte subsets in untreated systemic lupus erythematosus patients with infections

The leading cause of death in systemic lupus erythematosus (SLE) patients is infection. The objective of this study was to evaluate the distribution of lymphocyte subsets in untreated SLE patients with infections. This was a cross-sectional study. Data from January 2017 to May 2018 were collected. Flow cytometry was used to measure the peripheral lymphocyte subsets including CD3+T cells, CD4+T cells, CD8+T cells, CD19+B cells, CD3-CD16+CD56NK cells, and CD3+CD16+CD56NKT cells in 25 healthy controls and 52 treatment-naive SLE patients, among whom 13 were complicated with infections. Association between the lymphocyte subsets and infections was further analyzed. SLE patients with infections (n=13) showed a significantly higher incidence rate of fever (84.6 vs 28.2%) and serositis (84.6 vs 23.1%), increased level of erythrocyte sedimentation rate (60.5±30.1 vs 37.4±27.1 mm/h), serum C-reactive protein (CRP) (102.7±94.9 vs 9.4±14.9 mg/L), procalcitonin (PCT) (1.07±0.08 vs 0.16±0.13 μg/L), and lower blood hemoglobin (Hb) (93.0±20.5 vs 110.4±16.0 g/L) level compared with non-infection patients (n=39) (all P<0.05). In comparison with non-infectious SLE patients (387.9±261.6/μL), CD4+T cells count decreased significantly in infectious SLE patients (217.8±150.4/μL) (P<0.05), and it was negatively correlated with infection-related indicators including PCT (r=-0.573, P=0.041) and CRP (r=-0.596, P=0.032) levels. Our findings suggested that abnormalities of peripheral lymphocyte subsets were related to the immune disorder of lupus itself, regardless of immunosuppressive treatment. Monitoring lymphocyte subsets, especially CD4+T cells, may be helpful for identifying the presence of infection in SLE patients.