The B lymphocyte mitogens, bacterial lipopolysaccharide (LPS), pokeweed lectin, and tuberculin, induced proliferation in density-inhibited monolayer cultures of chick embryo fibroblasts. The stimulation was seen both as an early increase in sugar uptake and cell volume and later as an increase in thymidine incorporation and cell number. The concentration of LPS maximally stimulating fibroblasts was remarkably low, about 0.1–1 ng/ml. LPS preparation with very different sugar chains gave quite similar results indicating that the architecture of the hydrophilic carbohydrate part is not critical for the mitogenic effect.

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