The hyaluronidase associated with Treponema pallidum facilitates treponemal dissemination

Treponema pallidum contains hyaluronidase (Hase) associated with its surface. Experiments were performed to determine the functional role of this enzyme in syphilitic infection. The effects of incubating organisms with rabbit anti-bovine Hase or normal or immune sera were compared. Preincubation of treponemes with anti-Hase resulted in inhibition of treponemal degradation of hyaluronic acid, indicating that these antisera did in fact retard enzyme activity. Anti-Hase did not immobilize or neutralize T. pallidum. In addition, rabbits were immunized with bovine Hase and then challenged intradermally with organisms; subsequent lesion development was not affected. Anti-Hase did not block treponemal attachment to cultured testicular fibroblasts but did inhibit attachment to isolated capillaries. Rabbit amnions were used as an in vitro model for dissemination of T. pallidum. Anti-Hase retarded the penetration of organisms through the amnions. This inhibitory effect was dependent on the presence of amniotic hyaluronic acid. When this glycosaminoglycan was selectively removed, the anti-Hase lost its ability to inhibit treponemal penetration. When exogenous hyaluronic acid was added back to treated amnions, the inhibitory effect of anti-Hase was restored. Evans blue experiments were used to characterize treponeme-induced vascular leakage following intradermal inoculation of T. pallidum. Prior treatment of organisms with anti-Hase reduced dermal leakage of the dye, indicating the involvement of the treponemal Hase in causing vessel leakage. Finally, rabbit testicular infections were used as an in vivo model for dissemination; one testis was infected, and after 10 to 13 days, treponemes in the opposite testis were quantitated. The anti-Hase restricted dissemination of organisms. These findings point to the functional role of the treponemal Hase in facilitating disseminated syphilis.