For example, people who lack a particular blood group factor resist infection from just one of the four types of human malaria.

In addition to the Rh factor, two major blood group factors - A and B - determine blood types in people.

Blood group factor H has been reported to blind preferentially to endothelial cells as well as intestinal mucins and other glycoproteins.

"Dogs have about nine major blood group factors that have been identified, but only two have enough serious antigenicity to cause antibody production against it," he said.

Serial sections in 10 patients stained for the presence of blood group factor H (Fig 2A) showed that the staining pattern detected all endothelium whereas (Fig 2B) not all blood vessels stained positively with EGF, only those in the lamina propria.