VDRL ANTIBODIES ENHANCE PHAGOCYTOSIS OF TREPONEMA-PALLIDUM BY MACROPHAGES

Although reactivity in nontreponemal tests develops in patients with u ntreated syphilis, no immunologic function has been ascribed to these antibodies. This study demonstrates that rabbit antibodies induced by immunization with VDRL antigen and VDRL antibodies affinity-purified f rom syphilitic rabbit serum enhance phagocytosis of Treponema pallidum . The proportion of macrophages ingesting treponemes in the presence o f these antisera was 45% +/- 5% and 27% +/-4%, respectively, versus 14 % +/- 3% for normal serum (P < .001 and P < .01). Both IgG and IgM fra ctions contained opsonic activity. Absorption of VDRL antibodies from syphilitic serum diminished but did not eliminate opsonization, sugges ting at least two classes of target molecules. Despite opsonic capacit y, VDRL antibodies fail to facilitate macrophage-mediated killing of T . pallidum. Nevertheless, VDRL-immunized rabbits are partially protect ed against T. pallidum infection, developing fewer lesions (delayed an d smaller) than do unimmunized controls. These results suggest a heret ofore unrecognized functional role for VDRL antibodies in syphilis inf ection.