Immunoadjuvant Action of Liposomes: Mechanisms

Abstract

A large variety of antigens may initiate a series of events, finally leading to the production of specific antibodies by defined cells belonging to the B cell lineage of the immune system. The immunogenicity of these antigens may depend on different cellular requirements. Many antigens (e.g. proteins and erythrocytes) need the help of T-lymphocytes to start an immune response. These are referred to as thymus-dependent (TD) antigens which evoke a TD immune response. A number of other antigens have the capability to start an immune response without the help of T-lymphocytes. These are the thymus-independent (TI) antigens which evoke a TI immune response. Apart from T-lymphocytes and B-lymphocytes, most antigens require the participation of cells of the mononuclear phagocyte system (dendritic cells or macrophages). Although many immunologists nowadays seem to consider the immune response as a purely in vitro phenomenon, the immune system belongs in the body (Marx, 1985), where antigens, cells and their products have the opportunity to meet each other under optimum conditions. Evidence is growing that it is the microenvironment in a lymphoid organ, for which there is no in vitro equivalent, that creates the optimum conditions for the cells of the immune system to cooperate either directly or through their products. The possible cellular interactions during an immune response in the spleen and the localization and migration of the participating cells in defined splenic compartments have been recently reviewed (Van Rooijen et al, 1986). Herein we also postulated that there is a single differentiation pathway for all antibody-forming cells in the spleen, which is independent of the antigen and the type of immune response. We believe that this pathway is running along all of the different cells which may be required for any particular type of response.