T lymphocytes in acute bacterial infection: increased prevalence of CD11b(+) cells in the peripheral blood and recruitment to the infected site.

T-cell activation, particularly of CD8(+) cells, is invariably associated with viral infections. We now provide evidence for the activation of T cells in patients with localized bacterial soft tissue infections. During acute disease we detected in the peripheral blood of these patients, small though conspicuous populations of CD4(+) CD28(+) CD11b(+) and CD8(+) CD28(+) CD11b(+) cells, indicative of an expansion of effector T cells. Moreover, we identified CD4(+) and CD8(+) cells at the infected site, in addition to highly activated polymorphonuclear neutrophils (PMN). In keeping with their role as first-line defence, PMN were preponderant, but T cells amounted to 20% of the infiltrated cells. The majority of the infiltrated T cells expressed CXCR6, a homing receptor for non-lymphoid tissue. The infiltrated T cells produced interferon-gamma (IFN-gamma), while the peripheral blood cells obtained at the same time did not. In conclusion, in response to localized bacterial infections, T cells are activated and recruited to the infected site. We propose that these T cells, e.g. by producing IFN-gamma, enhance the efficiency of the infiltrated phagocytic cells, particularly of the PMN, thereby supporting the local host defence.

Activation of T Lymphocytes in Response to Persistent Bacterial Infection: Induction of CD11b and of Toll-Like Receptors on T Cells.

T cell activation is invariably associated with virus infections, but activation of T cells is also noted, for example, in patients with persistent bacterial infections with intracellular pathogens or localised bacterial biofilms. The latter is characterised by a destructive inflammatory process. Massive infiltration of leukocytes, predominantly of polymorphonuclear neutrophils (PMNs) and of T lymphocytes, is seen. While PMN influx into sites of bacterial infection is in line with their role as "first-line defence" a role of T cells in bacterial infection has not yet been delineated. We now found evidence for activation and expansion of peripheral blood T cells and an upregulation of Toll-like receptors 1, 2, and 4 on small portions of T cells. T cells recovered from the infected site were terminally differentiated and produced interferon gamma, a cytokine known to enhance functions of phagocytic cells, leading to the conclusion that infiltrated T cells support the local immuner defence.