Researchers have identified a promising new class of antibodies that protects against infection from HIV-1, the virus that causes AIDS.
The researchers from the Texas Biomedical Research Institute in the US used an animal model to show for the first time that an antibody called Immunoglobulin M (IgM) was effective in preventing infection after mucosal AIDS virus exposure.
Worldwide, an estimated 90 per cent of new cases of HIV-1 are caused through exposure in the mucosal cavities like the inside lining of the rectum or vagina, according to the study published in the journal AIDS.
"IgM is sort of the forgotten antibody," said Ruth Ruprecht, Scientist and Director of Texas Biomed's AIDS Research Program.
"Most scientists believed its protective effect was too short-lived to be leveraged as any kind of protective shield against an invading pathogen like HIV-1," Ruprecht said.
Scientists first treated rhesus monkeys with a man-made version of IgM, which is naturally produced by plasma cells located under the epithelium - the surface lining of body cavities.
Half an hour later, the same animals were exposed to SHIV (simian-human immunodeficiency virus). Four out of the six animals treated this way were fully protected against the virus. The animals were monitored for 82 days.
Ruprecht's team found that applying the IgM antibodies resulted in what is called immune exclusion.
IgM clumped up the virus, preventing it from crossing the mucosal barrier and spreading to the rest of the body.
The technique of introducing pre-formed antibodies into the body to create immunity is known as passive immunisation.
IgM has a high affinity for its antigens and "grabs them very quickly and does not let go," Ruprecht said.
"Our study reveals for the first time the protective potential of mucosal anti-HIV-1 IgM. IgM has a five-times higher ability to bind to virus particles compared to the standard antibody form called IgG. It basically opens up a new area of research. IgM can do more than it has been given credit," he said.
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