On day 1, 2, 3, 5, 7, 9, 11, 14, and 21, 2 mL of whole blood (EDTA-K2 anticoagulant) and 1.5 mL of serum were collected from H1N1 patients for the detection of lymphocyte subgroups, cytokines, and CRP. The same sample collection was carried out in the control group. Afterwards, 100 μL of anticoagulant was added into all flow tubes and 20 μL of CD3-PC5, CD4-FITC, CD8-PE, CD3-FITC-CD(16+56)-PE, CD19-FITC, and CD25-PE mouse anti-human fluorescence monoclonal antibodies (BD Bioscience) was added. After mixing, the samples were incubated for 15 min away from light at room temperature. Red blood cell lysis and cell fixation using Coulter QPREP specimen processing instrument (Beckman Coulter Inc., USA) was conducted, and the cells more than 1 × 10 4 were counted through a flow cytometer (Coulter Cytomics FC 500, Beckman Coulter). The results were expressed as the percentages of CD4 + CD25 + , CD4 + , and CD8 + T cells, as well as those of CD19 + B cells and NK (marked as CD3 -CD16 + CD56 + ) cells found positive for the antigen marker in the total lymphocytes population. The data were collected and analyzed using the EXPO32 software (Beckman Coulter Inc., USA).