Immunocytologic characteristics of mononuclear cell populations found in nonseptic olecranon bursitis

Objective. To determine the immunocytologic characteristics of the various subsets of nonseptic olecranon bursal fluid mononuclear cells. Methods. Twenty consecutive patients with culture negative olecranon bursitis had immunocytochemical and flow cytometric analysis performed using a panel of monoclonal antibodies to determine lymphocyte and monocyte/macrophage population subtypes and proportions. Results. In traumatic bursitis (n = 9), the mean (±SD) white blood cell (WBC) count/mm³ was 1,368 ± 1,559; WBC mononuclear differential count was 29.5 ± 19% lymphocytes and 55 ± 26% monocyte/macrophages. In idiopathic bursitis (n = 11), the mean WBC/mm³ was 376 ± 515; WBC mononuclear differential count was 28.5 ± 16% lymphocytes and 52 ± 27% monocytes/macrophages. Flow cytometry revealed 88% CD2+ T lymphocytes in the lymphocyte population, 3% B lymphocytes and CD4/CD8 T cell mean ratio of 2.5 ± 1.5 for traumatic bursitis and 88% CD2+ T lymphocytes, 4% B lymphocytes and CD4/CD8 ratio of 1.4 ± 0.6 for idiopathic bursitis (p < 0.05, t test). Both groups contained increased proportions of lymphocyte subtypes expressing activation markers: CD25+, CD26+ and HLA DR+ compared to normal peripheral blood. In traumatic bursitis, the mean percent of CD14+ cells (monocyte/macrophages) was 62 ± 24; in idiopathic bursitis, the mean percent was 51 ± 28. The vast majority expressed high levels of HLA-DR indicating activation. Conclusion. We observed a preponderance of activated T cell subpopulations and monocyte/macrophages suggesting an immunologic role for these cell populations in the development and perpetuation of nonseptic bursitis.