T cell and interferon-γ involvement in the adjuvant action of a detoxified endotoxin

The adjuvant activities of a detoxified derivative of endotoxic lipopolysaccharides, isolated from the outer membrane of gram-negative bacteria, were evaluated in aging mice. This monophosphoryl lipid A (MPL) (Ribi) was capable of enhancing antibody production in vitro in splenic cultures from 2-3-month-old male Balb/c mice as well as cultures from 22-24-month-old Balb/c mice. Separation of spleen cells from MPL and phosphate-buffered saline-injected mice into adherent and nonadherent populations and subsequent mixing of populations and culture with antigen implicated an adherent cell as being involved in the enhancement of antibody formation induced by MPL. However, separation of normal spleen cells into purified populations of adherent cells, T-lymphocytes, and B-lymphocytes, followed by in vitro stimulation of the individual populations with MPL and subsequent transfer into cultures of normal spleen cells, revealed only the T cell as capable of transferring the enhancement of antibody formation. In addition, culture filtrates from MPL-stimulated T cells were able to enhance antibody production by spleen cell cultures from aging mice twofold above that of filtrates from unstimulated T cells. The enhancement of antibody formation induced by such filtrates and also by MPL in spleen cell cultures from young and aging mice was inhibited by a monoclonal antibody (MAb) to recombinant interferon-γ (rIFN-γ) as well as an antiserum against IFN-α, -β, and -γ, but not by an antiserum to IFN-α/β. Enhancement of antibody formation correlated well with an increase in interleukin-1 (IL-1) but not with an increase in IL-2 production. Addition of anti-asialo-GM1 MAb plus complement to the effective spleen populations did not diminish the adjuvant action.