Induction of splenic T cell proliferation by lipid A in mice immunized with sheep red blood cells.

The stimulatory effect of alkali-treated lipid A on the in vivo proliferation of splenic T lymphocytes was investigated by determining 3H-thymidine incorporation into DNA after cell separation by nylon wool adherence. Our experimental model was the primary immune response against SRBC antigen. Mice received a single i.v. injection of alkali-treated lipid A 2 days post-immunization. The splenocytic IgG-plaque response was enhanced but the IgM-plaque response was not. On the 4th day postimmunization, 2H-thymidine uptake by the B cell population was not amplified. However, the splenocytic DNA content was increased in immunized, adjuvant-treated mice, and the radioactivity count in T lymphocytes of lipid A-treated mice was approximately twice that of lipid-untreated animals. We conclude that alkali-treated lipid A enhances T cell proliferation in mice immunized with red blood cells.