Surface molecules with the potential relevance for resistance against Mycobacterium tuberculosis were investigated. The expression of lymphocyte function antigen-1, very late antigen (VLA)-4, L-selectin, intercellular adhesion molecule (ICAM)-1, major histocompatibility complex class II, Fas, and CD40 on ab T cells, gd T cells, NK cells, and monocytes of healthy donors and patients with tuberculosis were analyzed. A high activation status of gd T cells and increased levels of soluble ICAM-1 in

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... lasma of patients with tuberculosis versus healthy individuals was detected. Tuberculosis patients with and without an underlying systemic disease could be segregated by differential expression of VLA-4 and ICAM-1 on gd T cells and on monocytes. The composition of peripheral blood mononuclear cells varied slightly, whereas the proportion of monocytes decreased significantly in patients with tuberculosis, compared with healthy controls. The activation phenotype of peripheral gd T cells in patients with tuberculosis emphasizes the role of these T cells in controlling the inflammatory process during tuberculosis and perhaps other microbial infections. Among human infectious diseases, tuberculosis remains the leading cause of mortality worldwide [1]. Case incidences in developing countries are exacerbated by poor social conditions and high human immunodeficiency virus (HIV) infection rates, and tuberculosis has reemerged in several industrialized countries. Besides HIV infection and alcoholism, systemic diseases such as diabetes mellitus, chronic gastritis, restricted liver and kidney function, and diseases requiring immunosuppressive therapy represent major risk factors for developing infectious diseases such as tuberculosis [1, 2] . Therefore, tuberculosis patients with or without underlying systemic disease are interesting research subjects for deeper insights into the immune response to Mycobacterium tuberculosis. Although CD4 ϩ ab T cells play a major role in acquired immunity to tuberculosis, gd T cells and CD8 ϩ ab T cells presumably perform complementary functions [2] [3] [4] . The ab T cells are the major population in peripheral blood, with an age-and sex-dependent CD4 ϩ /CD8 ϩ ratio. The CD4 ϩ ab T cells recognize mycobacterial peptides in the context of major histocompatibility complex (MHC) class II [3, 4] . T cells expressing gd T cell receptors comprise 1%-5% of circulating blood T lymphocytes.