Blood types, immune systems and personality

Many of us are fascinated by blood types. Do they affect our health? Do they affect our personality? Do they affect our choice of career?

There are many methods to classify blood groups. The principal method is to classify blood types into ABO groups. There are four main blood types, A, B, AB and O. From the naming system, you might suspect there is some structure about blood types. This is indeed the case.

People with type A and B can receive blood from people with the same blood type or type O. People with type AB can receive blood from anyone. People with type O can receive blood only from people with type O. Why is that?

This has something to do with our immune systems. Our bodies, and the bodies of any other life, are full of nutrients. Microbes want to suck nutrients from us. Our immune systems try to detect and destroy these invading microbes. At the same time, our immune systems need to recognize our own cells and avoiding attacking them. If microbes evolve similar structures to our own cells, our immune systems will not develop highly specific and highly effective antibodies to attack these invaders. However, our immune systems do have less specific and less effective cells to attack these invaders.

On the surface of blood cells of each type, there are type  specific protein molecules. Type A has A type molecules.  Type B has B type molecules.  Type AB has both A type and B type molecules.  Type O has none of these type specific molecules. As a result, people with blood type O developed type A and type B antibodies, people with blood type AB has neither type A nor type B antibodies, people with blood type A or B are in between.

Type A antibodies are hypothesized to originate from immune response towards flu virus. Type B antibodies are hypothesized to originate from immune response towards Gram-negative bacteria, such as E. coli. These research may suggest people with blood type A are more susceptible to flu infection while people with blood type B are more susceptible to disease from Gram-negative bacteria.

People with blood type O have both type A and B antibodies. With better immune protection, why these O type people don't replace all other people? This is because the specific molecules from type A and B perform useful functions for us. Statistics shows that O type people are more susceptible to cholera and some other diseases. The mechanism for that is not very clear.

From the above discussion, people with type O blood seem to have the most extensive immune systems while people with blood type AB have the most restricted immune systems. This might leads to certain personality traits. People with blood type O may be more outgoing while people with blood type AB may be more introvert on average. 

An empirical investigation can determine whether these theoretical deductions are valid. 

If some of the observations are true, they can be applied to our health cares. For example, people with type A blood should take more precaution against flu while people with blood type B should take more precaution against Gram-negative bacteria infection.

We may also apply our knowledge to career choices. For example, people with blood type O may be more capable in people oriented works while people with blood type AB may be more capable with technical works. These are just wild speculations that should be modified with more empirical and theoretical investigations.