Thursday, January 31, 2008

Got Blood?

A company in the US is using enzymes to convert blood cells with differing blood types (A, B, AB) to type O. This eliminates surface markers (i.e., antigens) on the red blood cells that can trigger an immune response when donor blood is transfused into a recipient. The company called ZymeQuest uses methods involving two enzymes from different bacteria to enzymatically remove the carbohydrate surface markers. This essentially makes any blood cell into type O which refers to the lack of A and B surface markers. Why is this important? Type O blood cells can be transfused into a person with any of the ABO blood types (A, B, AB, or O)... so having more type O blood would seemingly increase supplies of blood compatible with more people. Read more about ZymeQuest and their red blood cell conversion here.

A&P students might wonder, what about the Rh (D) antigen or surface marker? When the Rh antigen is present on red blood cells then the person's blood type is called "positive"... for example, red blood cells with the A antigen and Rh antigen are blood type A+ or A-positive. ZymeQuest doesn't seem to have found an enzyme to cleave off the Rh antigen. Ideally, the enzymatic conversion would strip both the A and B antigens as well as the Rh antigen, thus making treated blood a nearly universal donor supply... i.e., able to be donated into any blood type recipient. Remember, type O- or O-negative blood is considered the universal donor since these RBCs lack the A, B, and Rh surface antigens/markers.

What is the big deal? What happens to me if I get transfused with the wrong blood type? The short answer is that it depends, you could get mildly sick or in extreme cases you would die. eMedicine (topic: transfusion reactions) has the technical answers to this question:

Acute hemolytic transfusion that are immune-mediated (i.e., giving somebody the wrong blood type that reacts with antibodies in their plasma)

Immune-mediated hemolytic transfusion reactions caused by immunoglobulin M (IgM) anti-A, anti-B, or anti-A,B typically result in severe, potentially fatal intravascular hemolysis - so yes people can die from getting the wrong ABO blood type. Immune-mediated hemolytic reactions caused by immunoglobulin G (IgG), Rh (D) or other non-ABO antibodies typically result in shortened survival of transfused red cells, and relatively mild clinical reactions.

Acute hemolytic, immune mediated
: Most severe and fatal reactions result from inadvertent transfusion of group AB or group A red cells to a group O recipient. Renal failure and intravascular coagulation are potential complications for patients who survive the initial acute reaction. Fatal cases are 1 case per 250,000-600,000 so it seems rare.

It pays to be a baby... Because newborns do not form naturally occurring antibodies to ABO blood group antigens during the first few months of life, acute ABO-related transfusion reactions are not observed in this age group.