Syphilis is a sexually transmitted disease, and once acquired, progresses through a series of
overlapping stages. Data from a series of surveillance studies indicate that the acquisition of
syphilis may be altered by co-infection with HIV, suggesting that HIV infection decreases the
chances for infection with Treponema pallidum at the muco-cutaneous level.
This study, through the inoculation of keratinocytes with HIV and/ or T.pallidum,
investigated the effect of HIV infection of keratinocytes, on the transmigration abilities of
T.pallidum across a keratinocyte monolayer.
Using magnetically labelled antibodies specific for antigens in the viral envelope, infectious
HIV virions were isolated from blood. T.pallidum was harvested from the testes of rabbits in
which the organism was propagated. HaCaT cells were cultured on collagen-coated transwell
inserts, in 24-well tissue culture plates. Upon confluency, cells in one experiment were
inoculated first with HIV, and three days later with T.pallidum; cells in a second experiment
were exposed to T.pallidum first, and three days later inoculated with HIV; and cells in the
third experiment were exposed to both HIV and T.pallidum at the same time. The media
below the inserts, which contained the treponemes that passed through, was harvested at
different time points (24, 48, and 72 hours). For experiments one and two, post-inoculation
time points only took effect after inoculation with the second organism. DNA was extracted
using Probetec lysis buffer and quantitation was done by real-time PCR.
The number of treponemes that passed through prior HIV and T.pallidum infected
monolayers indicated little difference between the two culture conditions. The treponeme
numbers indicated an initial drastic decline, followed by a remarkable increase between 24
and 48 hours and a plateauing at 72 hours. However, transmigration through T.pallidum and
HIV exposed keratinocytes (experiment three), displayed a slight initial decline followed by a
drastic continuous increase in quantity till 48 hours post-infection, reaching significantly
higher levels, compared with experiment 1 and 2.
The results suggest that at the time HIV enters the keratinocytes, changes in the cell
membrane structure occur thus allowing for better adhesion and intake of T.pallidum;
therefore a higher transmigration rate. This observation may explain both a decrease in
primary syphilis in HIV endemic areas as well as the reported rapid progression to secondary
syphilis in patients with concurrent HIV infection. patients with concurrent HIV infection.||en