Bacterial Wall Components such as Lipothecoid Acid, Peptidoglycan, Liposaccharide and Lipid A Stimulate Cell Proliferation in Intestinal Epithelial Cells

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Earlier studies indicate that the microflora contains mitogens to intestinal epithelial cells. Our aim is to examine whether cell wall components of both Gram-negative and positive bacteria influence cell proliferation in small intestinal and colonic epithelial cells. A human colonic epithelial cell line from adenocarcinoma (IEC-6) and a nontransformed small intestinal cell line from germ-free rats (LS-123) were incubated with (a) lipothecoid acid from Streptococcus faecalis at 1.56–50 µ g/ml, (b) peptidoglycan from Staphylococcus aureus at 0.1 –7.5 µ g/ml, (c) lipopolysaccharides (LPS) from Escherichia coli , Klebsiella pneumonia and Pseudomona aeruginosa at 0.1 –7.5 µ g/ml, (d) lipid A from Escherichia coli at 0.016 –50 µ g/ml. The cells were labelled with tritiated thymidine and processed for autoradiography. DNA synthesis was estimated by the labelling index. Cell wall components of Gram-positive bacteria (LTA from Streptococcus faecalis and peptidoglycan from Staphylococcus aureus ) moderately increased the DNA synthesis in both cell lines (p<0.001). Similarly, cell wall components of Gram-negative bacteria (LPS of Escherichia coli , Klebsiella pneumonia and Pseudomona aeruginosa and lipid A of Escherichia coli increased the labelling index in IEC-6 and LS-123 cells (p<0.001). Thus, this study identifies mitogens present in both Gram-positive and Gram-negative bacteria that increase cell proliferation in rat and human intestinal cells. Our findings support a role for the microflora in the regulation of cell proliferation in both health and disease. Keywords: bacterial lipopolysaccharide, cell division, lipid A, lipothecoid acid, peptidoglycan.