Dynamics of Peripheral Blood Lymphocyte Subpopulations in the Acute and Subacute Phase of Legionnaires ’ Disease

Study Objective: Absolute lymphocytopenia is recognised as an important hallmark of the immune response to severe infection and observed in patients with Legionnaires ’ disease. To explore the immune response, we studied the dynamics of peripheral blood lymphocyte subpopulations in the acute and subacute phase of LD. Methods and Results: EDTA-anticoagulated blood was obtained from eight patients on the day the diagnosis was made through detection of L. pneumophila serogroup 1 antigen in urine. A second blood sample was obtained in the subacute phase. Multiparametric flow cytometry was used to calculate lymphocyte counts and values for B-cells, T-cells, NK cells, CD4+ and CD8+ T-cells. Expression of activation markers was analysed. The values obtained in the subacute phase were compared with an age and gender matched control group. Absolute lymphocyte count (6109/l, median and range) significantly increased from 0.8 (0.4–1.6) in the acute phase to 1.4 (0.8–3.4) in the subacute phase. B-cell count showed no significant change, while T-cell count (6106/l, median and range) significantly increased in the subacute phase (495 (182– 1024) versus 979 (507–2708), p = 0.012) as a result of significant increases in both CD4+ and CD8+ T-cell counts (374 (146– 629) versus 763 (400–1507), p = 0.012 and 119 (29–328) versus 224 (107–862), p = 0.012). In the subacute phase of LD, significant increases were observed in absolute counts of activated CD4+ T-cells, naı̈ve CD4+ T-cells and memory CD4+ T-cells. In the CD8+ T-cell compartment, activated CD8+ T-cells, naı̈ve CD8+ T-cell and memory CD8+ T-cells were significantl