Abstract
Endotoxin protein (EP) was isolated from the TCA-extracted lipopolysaccharide (LPS) of Salmonella minnesota R595 by the use of aquous phenol. The EP stimulated human B lymphocytes to synthesize DNA, even though T lymphocytes were depleted with the nylon column method, the E-rosetting method, or the mouse anti-human monoclonal antibody and complement. However, it is not concluded whether the EP is a human T-independent B cell mitogen or not, because it was not denied that a few T lymphocytes remained in the B lymphocyte fraction. The maximum uptake of 3H-TdR to lymphocytes was at 3 days after culture. The EP stimulated the lymphocytes from every human donors, and its stimulation was greater than that of LPS. Further, the EP produced the increase of immunoglobulin synthesis in human B lymphocytes.
Sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis revealed that the EP was heterogeneous protein, and its molecular weight was from approximately 10, 000 to 40, 000. Lipid A was detected in the EP by the limulus test, and the lipid A portion of the EP could be responsible for the mitogenic activity as well as LPS, since its mitogenic activity was inhibited by polymyxin B. It seems unlikely that the mitogenic activity of EP was due to the contamination by LPS, because the EP scarcely contained 2-keto-3-deoxyoctonate (KDO) which was reported to bridge between the polysaccharide and the lipid A in LPS.
