Experimental syphilis vaccines in rabbits. I. Differential protection with an adjuvant spectrum

This study shows that 1 per cent. glutaraldehyde fixation of unwashed Treponema pallidum, Nichols pathogen, preserves the integrity of the outer envelope as well as the ruthenium-red (RR) staining extracellular slime layer. Since other researchers wash their treponemal suspensions before preparing their vaccines, it is likely that the vaccine preparations used in this study contain antigens not tested elsewhere. In an attempt to eliminate the requirement of large numbers of injections to achieve any protection, the rabbits in this study were injected with glutaraldehyde-fixed T. pallidum (GFTP) only once, with or without one of a spectrum of adjuvants, and 5 months later were challenged intradermally or intratesticularly with freshly harvested pathogenic treponemes. Data of time of lesion appearance and severity of lesions reveal a differential protective effect of the various vaccine preparations when compared to the response of non-vaccinated controls. Vaccines which included phytohaemagglutinin (PHA) or alumina C gel (ALC) as adjuvants provided some degree of protection, whereas vaccines which contained the adjuvants incomplete Freund's, zymosan, complete Freund's, polyadenylic-polyuridylic acid, or no adjuvant at all produced enhanced infections. The differential protection data indicate that various portions of the immune mechanism are either suppressed or are not stimulated by T. pallidum antigens alone, but can be made to respond with a minimum of vaccine injections.