CD34(+) hematopoietic stem cells exert accessory function in lipopolysaccharide-induced T cell stimulation and CD80 expression on monocytes

CD34(+) hematopoietic stem cells, which circulate in peripheral blood with very low frequency, exert essential accessory function during lipopolysacch aride (LPS)-induced human T lymphocyte activation, resulting in interferon gamma production and proliferation. In contrast, stimulation of T cells by "conventional" recall antigens is not controlled by blood stem cells. These conclusions are based on the observation that depletion of CD34(+) blood s tem cells results in a loss of LPS-induced T cell stimulation as well as re duced expression of CD80 antigen on monocytes. The addition of CD34-enriche d blood stem cells resulted in a recovery of reactivity of T cells and mono cytes to LPS. Blood stem cells could be replaced by the hematopoietic stem cell line KG-1a. These findings may be of relevance for high risk patients treated with stem cells or stem cell recruiting compounds and for patients suffering from endotoxin-mediated diseases.