From today's Obgyn.net:
Why do most breastfed infants of HIV-positive moms resist infection?
Pediatric AIDS
December 22, 2003
http://www.obgyn.net/newsheadlines/headline_medical_news-Pediatric_AIDS-20031222-6.asp
Although prolonged breastfeeding is well known to be a major route of
transmission of HIV infection to infants and is estimated to cause
one-third to one-half of new infant HIV-1 infections worldwide, the
majority of breastfed infants with HIV-positive mothers remain
uninfected, even after months of exposure.
Investigators at Emory University School of Medicine, the U.S.
Centers for Disease Control and Prevention, the Emory Vaccine Center
and the University of Paris reviewed the scientific literature to
pinpoint the reasons why many breastfed infants resist HIV, with the
goal of devising future intervention strategies to prevent newborn
infections. Their findings are published in the December 2003 issue
of the Lancet Infectious Diseases.
The researchers, led by Athena P. Kourtis, MD, PhD, MPH, formerly
assistant professor of pediatrics at Emory University School of
Medicine and now at CDC, and Chris Ibegbu, PhD, of the Emory Vaccine
Center, identified several factors that have been cited by scientists
as potentially enabling or preventing transmission of HIV through
breastfeeding. Enabling factors could include the introduction of HIV
into the gastrointestinal tract through a breach in the cell layer in
the intestinal lining, or immune activation in the gastrointestinal
tract could cause more HIV virus to reach this epithelial layer.
Protective factors may include the hostile environment presented to
viruses by the saliva and its various viral-inhibiting components.
The presence of HIV antibody in saliva already has been recognized in
HIV-infected individuals, but scientists do not yet know whether this
antibody is developed in noninfected breastfed infants, or whether it
has a protective role against HIV. Natural killer (NK) cells or
natural antibodies to HIV in exposed mucosal surfaces of infants
could also play a role in resistance to HIV infection. Acquired
T-cell responses or specific antibody responses also may play a
preventive role. Immune CD4 and CD8 T cells and antibodies in the
mother's milk have been studied as factors that could account for
this protection.
"In the developed world, where alternatives exist, breastfeeding is
not recommended for HIV-positive mothers, which in part explains our
lack of knowledge about resistance to infection," Kourtis said. "In
the developing world, however, breastfeeding often is the only
practical option for feeding infants, which makes understanding the
mechanisms of HIV transmission a research priority. Inconsistent
research findings about the role of anti-HIV antibodies and
HIV-specific T-cell responses have left significant gaps in our
understanding of HIV transmission through breastfeeding."
Kourtis believes that advances in laboratory methods will help
scientists clarify which immune factors are most important in HIV
protection and help in the development of carefully planned
intervention strategies. These could possibly include giving
antibodies to the mother in late pregnancy or to the newborn,
together with antiretroviral prophylaxis, she explained. Some of
these approaches will be tested soon in large international trials.
This article was prepared by AIDS Weekly editors from staff and other
reports.
©Copyright 2003, via NewsRx.com & NewsRx.net
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