Now a protein can boost immune system's ability to fight against pneumonia, claim researchers in a new study.
The finding may offer a new way for doctors to boost patients' ability to fight off the life-threatening infection as bacteria become more and more resistant to antibiotics.
"We're interested in seeing if there are things we can do to strengthen the natural defences of the host to help them fight the infection more effectively," said Borna Mehrad from University of Virginia School of Medicine.
"Potentially this would be the sort of thing you could do in addition to antibiotics to help patients with severe infections," Mehrad noted.
Mehrad and his team determined that the lack of the cytokine M-CSF (short for macrophage-colony stimulating factor) in infected mice worsened the outcome of bacterial pneumonia.
Not having the protein resulted in 10 times more bacteria in the lungs, 1,000 times more bacteria in the blood and spread the infection to the liver, resulting in increased deaths.
Clearly M-CSF has an important role in battling pneumonia, but what exactly does it do?
"M-CSF has previously been shown to help make a type of immune cell, called monocytes, so my idea was that if you take it away, infected hosts just stop making monocytes and that's why they get sick, and it turned out that was completely wrong," Mehrad said.
Instead, the findings published in The Journal of Immunology showed that M-CSF helped monocytes survive once they have arrived in the infected tissues.
"If you take M-CSF away, the infections get worse, so that raises two important questions about therapy: Would more be better? It may be that during infection, the body is making the right amount of M-CSF and if we add extra, it won't improve outcomes further," Mehrad said.
"The second possibility is that there is room for improvement: in the fight between monocytes and the bacteria, M-CSF may make monocytes live longer and give them an edge. In addition, some people with weakened immunity might not make enough of M-CSF. If that's the case, you could augment that and improve their ability to fight the infection," Mehrad explained.
(With Agency inputs)