A bird macrophages infected with the fungal pathogen Cryptococcus neoformans (green).

Birds are known to carry Cryptococcus neoformans, a fungus that causes fatal infections, such as AIDS, in those with a weakened immune system. It has also been a longstanding mystery why the birds themselves do not appear to become ill. A new study, however, offers some clues.

Researchers from the University of Sheffield and the University of Birmingham in the United Kingdom have shown that a particular white blood cell within the bird’s blood system, called a macrophage, is able to completely block the growth of Cryptococci.

The study was published on Feb. 17 in Nature Scientific Reports.

In the study, the researchers found that the fungus can grow slowly within the bird’s digestive tract, but if it tries to invade the bird’s body, the immune system immediately destroys it, which explains why healthy birds can still help spread the infection. 

“Birds have a higher body temperature than humans, 42 ^oC instead of 37 ^oC,” said Simon Johnston, PhD, and one of the study authors, “ but this alone is not enough to fully stop the fungus.

“By studying bird cells under the microscope, we have seen that macrophage cells have the ability to completely block the growth of the fungus….” 

Photo credit: University of Sheffield