The highly dreaded, most common sexually transmitted disease (STD) chlamydia has boggled the minds of many for as long as 50 years now. Researchers have done experiments to try to find a way to prevent this disease. After nearly half a century, scientists have now found a way to fight it.

Chlamydia, an infection caused by the bacteria Chlamydia trachomatis, spreads throughout around 100 million people worldwide each year. It is known to be the number one cause of infertility and ectopic pregnancy and can highly result in preventable blindness. Chronic inflammation may spring from chlamydial infection, badly affecting mucosal surfaces, such as the eyelids, ovaries or fallopian tubes. For most people, they do not realize they have been infected by the sneaky bacterium until they have been tested.

As early as the 1960s, scientists have tried to come up with ways to protect people against the infection. The idea of immunization against chlamydia was first put to test when experts experimented with killed chlamydia. The experiment did not come up with positive results.

Tweaking the experiment slightly, experts at the Harvard Medical School conducted another study. They now present what is believed to be a solution to the longstanding problem that is chlamydia.

The researchers set up an experiment similar to that of the 1960s, using mice as subjets. They gave some a dose of killed chlamydia bacteria and others a dose of live bacteria. The subjects that were then given killed bacteria were found to be more likely infected than those given live chlamydia.

This experiment found that T lymphocyte, a specific type of white blood cell, was responsive to the bacteria. Immune responses to live chlamydia differed from responses to killed bacteria.

"When they're stimulated by Chlamydia, they can sort of make different career decisions," explained immunologist Ulrich von Andrian at Harvard. Regulatory T cells are anti-inflammatory. They prevent the immune system from fully acting against allergens.

The scientists further mixed the vaccine with immune-response boosting substances called adjuvants, but the T cells exhibited the same reaction. They found that mixing these particles had no effect on the T cells' "career path."

The researchers were then led to apply nano-particle science to the experiment, similar to how a surgeon would use tiny biodegradable plastic to make dissolvable sutures. The T cells chose "better career paths" when the adjuvants stuck to the vaccine, thanks to the nano-particles with a positive charge. In essence, this applied the idea that all living cells carry negative charges on their surfaces.

"We thought, perhaps we can exploit the fact that this killed Chlamydia is actually seen by the immune system and attach a message to this killed Chlamydia, such that the response becomes a desired one," said von Andrian.

A more detailed explanation of the study is published in the journal Science.

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