An international team of researchers from Canadian Blood Services, The Hospital for Sick Children in Toronto and Lund University in Sweden have discovered that certain blood types are more predisposed than others to contracting HIV, while some are more effective at fending it off.

The study, published online in the journal Blood, found a carbohydrate-containing antigen, termed Pk blood group, is present at variable levels on the surface of white and red blood cells in the general population. The researchers said cells from some people who produce excess of this blood group antigen have dramatically reduced sensitivity to HIV infection. Conversely, another slightly more common subgroup of people who do not produce any Pk was found to be much more susceptible to the virus.

"This study is not suggesting that your blood type alone determines if you will get HIV," lead author Dr. Don Branch of Canadian Blood Services said in a statement. "However, it does suggest that individuals who are exposed to the virus, may be helped or hindered by their blood status in fighting the infection."