Researchers at the University of Texas (UT) Southwestern Medical
Center in Dallas are offering the first plausible, molecular
explanation of the behavior of the human immunodeficiency virus (HIV)
in people with syphilis. The virus is transmitted more easily to or
from people infected with syphilis. This knowledge could lead to
treatments that slow the progression of HIV disease, they say.
"Syphilis, too, is a chronic, systemic illness in which the
bacteria migrate rather freely throughout the body causing
inflammation at numerous sites," said Dr. Michael Norgard,
acting chairman of microbiology at UT Southwestern Medical Center.
"By estimating what probably occurs in the genital ulcers caused
by syphilis, we surmise that systemic levels of bacteria from that
disease may actually activate immune cells throughout the body.
Higher levels of HIV, which then result, could interfere with the
efficacy of HIV treatment and even accelerate the course of AIDS."
Latent HIV Gene Expression
In a collaborative effort, Drs. Richard Gaynor and Justin Radolf,
scientists in the laboratories of Dr. Norgard and professors of
internal medicine and microbiology, looked at immune cells in
laboratory dishes to determine whether the syphilis bacterium or its
membrane lipoproteins could trigger latent HIV gene expression. Drs.
Gaynor and Radolf were interested in seeing whether gene expression
appeared in the primary genital ulcers, or chancres, of syphilis.
"We think the lipoproteins, a class of cell-membrane proteins in
the syphilis bacterium, predominantly cause the inflammatory
processes that typify the disease," said Dr. Norgard. "What
is implied in our findings is that syphilis may predispose a person
toward more rapid progression of HIV disease," he said.
No other studies of the effect of syphilis on the progression of HIV
into acquired immunodefiency syndrome (AIDS) have been done. What is
known, however, is that patients with chronic secondary infections
associated with AIDS exhibit higher HIV levels because of the
constant stimulation of the bodys immune system.
"This research is especially significant because we combined two
areas of molecular biology--HIV and syphilis--so that we could
develop experimental models and determine more fully the association
between the two diseases," said Dr. Radolf.
Connection Between HIV and Syphilis
According to the Centers for Disease Control and Prevention (CDC),
people with syphilis are two to five times more likely to transmit or
contract HIV than are individuals not infected with a sexually
transmitted disease. Epidemiologic studies have attributed this
phenomenon to the open sores on the genitals or oral cavities of
people with syphilis.
Future research could involve a clinical study designed to find out
whether patients infected with both HIV and syphilis have higher
levels of the virus before they are treated for the syphilis
bacterium. Identifying people with syphilis, however, is more
difficult than curing them because many people avoid seeking help due
to fear, lack of money, or the absence of convenient medical facilities.
Syphilis has a long progression and can lay dormant for years if
untreated. If the bacterium enters the nervous system, it can lead to
blindness, impotence, or insanity and can be fatal. But the disease
is usually curable with an intramuscular injection of a slow-acting penicillin.
Although the number of cases of syphilis in the United States have
declined steadily over the past few years, it remains a major
public-health problem. The CDC reports that the disease is more
prevalent among blacks, and the region of the country with the
highest rate of the disease, the South, is also the area with the
largest number of heterosexually transmitted cases of HIV. According
to Dr. Anthony Fauci, director of the National Insititute of Allergy
and Infectious Diseases, the number of HIV cases transmitted through
male-female sexual contact in the United States increased from 4.8%
in 1988 to 20.3% in 1997. About 860,000 US residents have the AIDS virus.
"Our research is a first step toward understanding the molecular
events that may trigger activation of the immune cells that support
HIV replication in the setting of syphilis co-infection," said