Bacterial infections are normally countered by white blood cells called neutrophils in the body. These cells travel through the blood stream to the tissue that is infected with the bacteria to kill it. The cells build the immunity level of the body but their life span is short and so new neutrophils are continuously generated by the body. The stem cells in the bone marrow controls and regulates the production of the white blood cells.

"We know that the protein CEACAM1 is involved in the regulation of white blood cells, but its specific role in neutrophil-dependent host immune responses has not been investigated," explains senior study author, Dr. John E. Shively from the Beckman Research Institute of City of Hope in Duarte, California. "We were interested in determining what would happen to neutrophil-mediated immunity in mice that did not express CEACAM1." They found that the mice models under observation are lacking CEACAM1 and had an excess of neutrophils.

They also found that the excess neutrophils found in the body did not present any extra protection. Interestingly, the mice infected with Listeria and lacking CEACAM1 died faster than the control mice. The study also shows that the mice which lack CEACAM1 have better bacterial clearance. However, they were found to be suffering from extreme damage to the liver tissue.

Combination of high levels of neutrophil-secreted chemicals damaged the liver and induced accelerated mortality in Listeria-infected mice lacking CEACAM1 was the conclusion of the research. "The insights from our work highlight the importance of natural mechanisms that restrain white blood cell proliferation and may have clinical implications in treating infectious and auto-inflammatory disorders," says Dr. Shively.