TraT: a powerful carrier molecule for the stimulation of immune responses to protein and peptide antigens.

A number of integral membrane proteins (Imps) isolated from Escherichia coli have been examined for their ability to generate serum antibody responses in the absence of adjuvant. These proteins were found to stimulate high titers of serum antibody when injected into rabbits or mice in saline. The antibody titers elicited were not significantly increased by the addition of a powerful adjuvant such as IFA. Covalent conjugation of BSA, of the DNP group, and of a peptide Ag from Plasmodium falciparum to these protein carriers resulted in a significant enhancement of the immune response to the conjugated material in comparison with the response elicited when the immunogen was injected without adjuvant or was not conjugated to Imps. The antibody response to these conjugates could not be significantly increased by the addition of IFA. Thus, the Imps of E. coli represent powerful carrier molecules which, when injected into mice and rabbits, are not only capable of generating high titers of antibody to themselves, but also to molecules conjugated to them. Immunization with immunogens coupled to these proteins results in the production of high titers of antibody without the need for oil-based adjuvants, thereby avoiding the unwanted side effects of such adjuvants.