Aust'n researchers discover immune cells to fight Legionella bacteria

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A team of Melbourne researchers believe they have discovered a new immune cell which is able to fight the infectious and potentially lethal bacteria, Legionella.

A team of specialist immunologists and microbiologists from the University of Melbourne and the Peter Doherty Institute for Infection and Immunity conducted a study which was able to determine a new cell type responsible for combating the attack of the bacteria.

The team was able to break down the impact of the legion of immune cells in the lung, which communicate to destroy the legionella bacteria.

Legionnaires' Disease is a severe form of pneumonia, which is caused by the bacterium known as Legionella Pneumophila. The fatality rate has ranged from 5 to 30 percent during various outbreaks and can approach 50 percent when treatment with antibiotics is delayed. Hospital-acquired Legionella pneumonia has a fatality rate of 28 percent.

Legionnaires' disease does not spread from one person to another in most cases. Rather, most people contract the infection from inhaling the bacteria, which filters into the lungs. Legionella can be found in contaminated water sources, such as spas.

In May this year, a New South Wales man died from the disease after there was a Legionnaires' outbreak in Sydney's CBD.

University of Melbourne PhD student, Andrew Brown, was a part of the team that led the study. Brown researched the activity of the lung when infected with Legionella bacteria, after reading a recent Belgian study on immune cell populations in inflamed tissue.

Brown found a new population of immune cells - the monocyte-derived cells (MCs) that exuded a major response to Legionella within 24 hours of infection. The MCs surfaced more than 10 times the number of macrophages (important cells of the immune system that are formed in response to an infection) in the lung by 48 hours after infection.

In a University of Melbourne media release on Thursday, Brown said it was a "surprising find" that the MCs, rather than the macrophages, were able to absorb and control the bacteria.

MCs are the first form of the immune system's defence against bacteria. In this study, the MCs responded to the infection and discharged a chemical messenger, which in turn sent another powerful chemical messenger to the immune system, and initiated the MCs to kill and overwhelm the Legionella bacteria. All of this happened within 48 hours.

"As immunologists, we usually look at what is happening in the immune organs, such as the bone marrow, lymph nodes and spleen, but in this study, we decided to look at what was happening in the tissue at the site of infection," said the team's lead researcher, Professor Ian van Driel.

"With a knowledge of the immune cell circuitry involved in defence against Legionella, we can understand what an effective immune response looks like," said the Doherty Institute's Professor Elizabeth Hartland on Thursday.

"Knowing this, we can now focus on how to manipulate and optimize the immune response to fight infection."

"With the rise of antibiotic resistance, this knowledge provides avenues for a different approach to fighting acute lung infections, by strengthening the immune system, as well as dispensing antimicrobial agents. It may also allow us to give patients a more accurate prognosis for the infection, giving us vital information about when to use antibiotics." Endit

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