(A) Typical flow cytometry analysis of CD11b and CD14 expression on the surfaces of monocytes from a patient with sickle cell disease and a normal subject.

Leukocytes were obtained from blood after the lysis of RBCs. They were immunostained for the surface expression of CD11b and CD14. Immunostained monocytes were analyzed by flow cytometry. A gate was placed around the mononuclear leukocytes based on their forward and side scatter. Monocytes within that gate were identified based on their expression of CD14-specific immunofluorescence. The crosshatch separates specific and nonspecific immunofluorescence. Cells to the right of the crosshatch are CD14⁺ monocytes, and cells above the crosshatch are CD11b⁺ monocytes. Monocytes in the upper right quadrant are activated, and monocytes in the lower right quadrant are resting. In this example, based on CD11b surface expression, 97% of the patient's monocytes are activated and 3% are resting; 37% of the normal subject's monocytes are activated and 63% are resting. (B) Sickle monocytes are activated: summary of CD11b flow cytometry results. Expression of CD11b and CD14 on monocytes was measured by flow cytometry in 9 patients and 11 normal subjects, as described in A. Results are presented as the percentage of CD14⁺ monocytes that are CD11b⁺. On average, 62% of sickle monocytes were activated as judged by CD11b surface expression compared to only 19% of normal monocytes (P = .002). Six of the 9 patients were admitted to the hospital for pain crisis. Surface expression of monocyte CD11b in the crisis (P = .029) and noncrisis patient groups (P = .007) was statistically greater than normal.