HIV-uninfected babies born to mothers with HIV have fewer antibodies, study shows
9 February 2011
The finding, published this week in the 'Journal of the American Medical Association', may help to explain why uninfected babies born to women with HIV have a higher risk of illness and death early in life.
Major programmes using antiretroviral drugs have successfully reduced the rate of mother-to-child transmission of HIV from around one in four to around one in twenty in some areas of South Africa and to less than one in a hundred in high-income countries. Uninfected infants born to HIV-infected mothers in Africa, however, are more prone to infections such as pneumonia and meningitis and are up to four times more likely to die before their first birthday than babies born to uninfected women. Socioeconomic factors are thought to account partially for this discrepancy, but differences in the babies' immune systems might also be important.
The new study, by scientists from Imperial College London and Stellenbosch University in South Africa, found that babies born to HIV-infected mothers had significantly lower levels at birth of antibodies against a range of bacterial infections, such as Haemophilus influenzae type B, pneumococcus and tetanus.
Antibodies, which bind to specific pathogens and direct immune cells to attack them, are transferred from mother to child through the placenta late in pregnancy. The study found lower levels of some specific antibodies in mothers with HIV and also found that fewer antibodies are transferred from mother to child across the placenta.
Despite their low antibody levels at birth, the babies in the study responded well to vaccination: they produced similar levels of antibodies to some vaccines and higher levels to other vaccines.
"It's likely that lower antibody levels in these babies contribute to lower protection against infection before the babies have received their vaccines," said Dr Christine Jones from Imperial College London, the study's first author. "Although they appear more vulnerable in the first few months of life, the good news is that these babies respond well to vaccination. We might be able to protect them even better against infections, either by vaccinating them earlier or by vaccinating the mother in pregnancy."
The study involved 109 HIV-infected and uninfected mothers in a community health centre in Khayelitsha, a rapidly growing township in Cape Town, South Africa. The researchers measured antibody levels in the mothers at delivery and the infants at birth. They also assessed how the babies responded to routine vaccination by measuring the babies' antibody levels at four months, after they had received their routine vaccines.
Among the HIV-negative women in the study, one-third also had low antibody levels, showing that protection against infection might not be optimal in the babies of some women who are otherwise perfectly healthy.
Dr Beate Kampmann, senior author of the study, said: "Around six million children under five die every year from infectious diseases, and a lot of these deaths are preventable by using existing vaccines. Studies like ours are helping us understand why certain infants might be especially susceptible to infections, and how we might tailor vaccination policies to protect vulnerable babies more effectively."
The study was supported by funds from the European Society for Paediatric Infectious Diseases, the Thrasher Research Foundation, the Elizabeth Glaser Pediatric AIDS Foundation and the Wellcome Trust.
Image: Maamohelang Hlaha, who is HIV positive, kisses her HIV-uninfected son Rebone. Credit: Reverie Zurba/USAID (found via usaid.africa on Flickr).
Reference
Jones C et al. Maternal HIV infection and antibody responses against vaccine-preventable diseases in uninfected infants. JAMA, 2011; 305 (6): 576-584
