Human afferent lymph from normal skin contains an increased number of mainly memory/effector CD4(+) T cells expressing activation, adhesion and co-stimulatory molecules

We investigated the T cell population in the afferent lymph and the periphe ral blood with regard to expression of activation, adhesion and co-stimulat ory molecules and cytokine profile by immunohistochemistry and flow cytomet ry. The majority of the lymphoid cell population in the afferent lymph were CD4(+), CD45RO(+) T cells expressing the alpha beta TCR. An increased perc entage of the T cells expressed activation molecules like HLA-DR, CD25, CD2 6, CD69 as well as adhesion and co-stimulatory molecules like CD54, CD154/4 0 ligand. Furthermore, T cells in the afferent lymph predominantly expresse d the type 1 cytokine IFN-gamma, whereas type 2 cytokines such as IL-4, IL- 5, IL-10 were not or barely detectable. Interestingly, dendritic cells expr essing IL-12 were also found in close association with some lymphocytes, in dicating that these contacts may be important in promoting Th 1 cells. In c onclusion, an increased number of mainly CD4(+) memory/effector T cells, ex pressing activation, adhesion and co-stimulatory molecules migrate through the afferent skin-derived lymph in humans. Furthermore, our data demonstrat e the dominance of a type 1 cytokine profile in these T cells and suggest t hat they have an important function in the immune surveillance against path ogens or other antigens in the skin and its associated lymphoid tissue.