Lipid A induces cells, uniquely present in bone marrow, to secrete proteins other than immunoglobulins.

The lipid-A moiety of lipopolysaccharide induced freshly isolated bone marrow cells incubated with radioactive leucine to exhibit enhanced release of proteins other than immuoglobulins. Such stimulation by lipopolysaccharide was essentially not observed with cell suspensions from spleen, thymus, appendix, peritoneal exudate, whole blood, lymph node, liver, testis, buffy coat of blood and reticulocyte-enriched blood. The extracellular appearance of proteins was shown to be due to secretion by excluding other alternatives. Thus, the rate of cell death and/or leakage of cellular contents, as well as the rate of shedding of surface membrane protein, was unaffected measurably by lipopolysaccharide. Secretion of non-immunoglobulin proteins was selective as judged by the finding that the rate of immunoglobulin released by bone marrow cells during the usual four-hour pulse-label period was not stimulated by lipopolysaccharide. Enhancement of mitogenesis and enhancement of secretion of non-immunoglobulin protein by lipoplysaccharide appeared to occur at independent sites or even in different cells because of splenocytes which readily exhibited mitogenic response to lipopolysaccharide essentially did not exhibit stimulatin of secretion of non-immunoglobulin protein.