| Abstract: | Lipopolysaccharide (LPS) was analyzed in order to determine which component, lipid A or polysaccharide (PS), is able to stimulate B lymphocytes from ICR lymph nodes and spleen cells from nude (nu/nu) mice into forming colonies in soft agar culture. Lipid A, obtained by acid hydrolysis of LPS and solubilized by complex-formation with bovine serum albumin, was found to be the active moiety of LPS capable of stimulating colony growth of lymphoid cells in soft agar culture. The PS portion exhibited no significant activity at the concentrations used. Glycolipids from mutant strains of S. minnesota which contain the intact lipid moiety but are deficient in PS content, were as potent as S. abortus equi LPS in stimulating B cells into colony growth. Alkaline hydrolysis of LPS which cleaves ester-linked fatty acids, substantially decreased the number of lymphocyte colonies formed. This indicates that the intact lipid moiety is required for stimulating lymphocytes into colony formation. The synthetic glycolipid, N-palmitoyl-D-glucosamine (NPG), whose structure is similar to some components of lipid A, was also able to induce B lymphocyte colony development. In summary, our data point to lipid A as the active moiety of the endotoxin which induces B lymphocytes to grow and develop into colonies in the 2-layer soft agar culture system. |
