Last weekend vampires and witches came out to play. People smeared litres of fake blood on their faces and doors. But for some people, there was no Halloween this year.
Many people across the world depend on blood transfusions. However, for a lot of people, blood transfusions are either not available or are not safe. The necessity for transfusion can stem from accidents and injuries to lifelong genetic conditions. While the need for blood is universal, access to blood is sadly not. Around 118.4 million blood donations are collected worldwide. Of these, 40% are from high-income countries, home to 16% of the world’s population. There is a marked difference in the level of access to blood between low- income and high-income countries.
In this blog, we explore the genetics of the blood system, including rare types, and the influence of blood on disease and health. Additionally, we will look at the impact of blood donations and the necessity for wider access to blood.
The blood system
Blood is a bodily fluid that delivers necessary substances, such as nutrients and oxygen, to cells. It also transports metabolic waste products away from those same cells. Blood in vertebrates consists of blood cells suspended in blood plasma. Blood cells mainly include red and white blood cells and platelets. Plasma constitutes 55% of blood fluid and is mostly water, yet also contains proteins, glucose and other important molecules.
Currently, the International Society of Blood Transfusion has recognised over 30 blood group systems, which represent over 300 antigens. The molecular mechanisms responsible for these polymorphisms are diverse. We describe some of the most important systems below.
Karl Landsteiner in 1990 discovered the ABO blood group system, which he won the Nobel Prize for in 1930. It remains the most important system in transfusion and transplantation. The system consists of four types. Blood group A contains antibodies against blood group B in serum and vice-versa. While blood group O contains no A or B antigen but both of their antibodies in serum. Finally, blood group AB have both A and B antigens and therefore, have no antibodies in their plasma.
H-antigen is the precursor to the ABO blood group antigens. It is present on all red blood cell surfaces, regardless of the ABO system. Individuals with the rare Bombay phenotype are homozygous for the H gene and do not express H-antigen on their red blood cells. As a result, there is an absence of antigens A and B.
This is the second most important blood group system. It consists of 50 defined blood group antigens of which only five are important. The surface of a red blood cell may or may not have Rh factor or immunogenic D-antigen. Status is as follows: Rh-positive (D-antigen present) or Rh-negative (D-antigen absent). Anti-Rh antibodies are typically not present in the blood of individuals with D-negative red blood cells, unless the individual has been exposed to D-positive red blood cells. Healthcare professionals provide prophylactic anti-D immunoglobulins to pregnant Rh-negative mothers who have given birth to Rh-positive children.
Experts define these erythrocyte antigens by an immune antibody, anti-K. To date, researchers have discovered 25 Kell antigens. Anti-K antibodies cause severe haemolytic disease of the foetus and newborn. They are the third most potent immunogenic antigen after ABO and Rh systems.
The Duffy antigen also known as Fy glycoprotein is present on the surface of red blood cells. It is a nonspecific receptor for several chemokines and the receptor for the human malarial parasite Plasmodium vivax.
Association with disease
Our blood type is not only important for ensuring safety of blood transfusions, but can also make us more susceptible to disease.
There are a range of blood disorders, the most prominent being haemoglobinopathies. These are a group of blood disorders and diseases that affect red blood cells. Moreover, in most cases, they are single-gene disorders that are inherited as autosomal co-dominant traits. The most common haemoglobinopathy is sickle-cell disease (SCD). SCD are a group of blood disorders, the most common being sickle cell anaemia. Experts characterise it by a sickle-like shaped blood cell and abnormality in oxygen-carrying. Estimates indicate that 7% of the world’s population are carriers, with the majority found in sub-Saharan Africa.
Another important genetic disorder is haemophilia. It is a disorder that impairs the body’s ability to make blood clots. This results in people bleeding for longer periods of time after injury. There are two main types of haemophilia. Haemophilia A occurs due to low amounts of clotting factor VIII, while haemophilia B occurs due to low levels of clotting factor IX.
Another blood disease is leukaemia – a group of blood cancers that usually begin within the bone marrow. They arise from the accumulation of high numbers of abnormal blood cells that are not fully developed. There are four main types of leukaemia: acute lymphoblastic leukaemia, acute myeloid leukaemia, chronic lymphocytic leukaemia and chronic myeloid leukaemia. Healthcare professionals often give blood transfusions to cancer patients to treat anaemia associated with leukaemia.
Susceptibility to infection
Since the discovery of the ABO blood system, there has been an ongoing interest in the potential role of blood groups in infectious diseases. Many blood groups act as receptors for toxins, parasites and bacteria. Most importantly, some bacteria can stimulate antibodies against blood group antigens. Below we describe some examples of innate resistance to infectious diseases:
- Carriers of the sickle-cell anaemia trait are resistant to infection by Plasmodium falciparum, hence its high frequency within malaria-endemic regions.
- The rare Dantu blood variant, commonly found in parts of East Africa, provides protection against severe malaria.
- Red blood cells that lack the Duffy antigen are relatively resistant to invasion by Plasmodium vivax and Plasmodium knowlesi.
- One of the first studies to associate ABO type and cholera was in 1977. They found that individuals with type O blood are the most susceptible to infection.
- Since its emergence late last year, several studies have explored the impact of blood type on susceptibility to infection. Most studies suggest that, like the original SARS-CoV, individuals with type O blood are less likely to be infected with the virus.
Giving blood saves lives. And knowing your blood type can be critically important too. There is a growing demand for better-matched blood, with calls for more diverse donors. Nearly 400 new donors a day are needed to meet current demands.
It typically takes four to eight weeks for your body to completely replace its red blood cells. This means an individual can donate whole blood every 56 days. Estimates indicate that women give 33% of blood donations globally. In addition, studies have found that more young people donate blood in low and middle-income countries than in high-income countries.
An ongoing concern, particularly in low-income countries, is the transfusion of unsafe blood. Unnecessary and unsafe transfusion practices expose patients to the risk of adverse reactions and infections. Unnecessary transfusions also reduce the availability of blood products for patients who need it. WHO recommends the development of systems, such as hospital transfusion committees and haemovigilance, to monitor and improve the safety of transfusion processes.
Blood donation schemes are incredible. However, in recent years, they have come under scrutiny due to issues of prejudice. In the UK, homosexual men were only allowed to donate blood in 2011. There are still criteria for gay and bisexual men which prohibits them from giving blood if they have had oral or anal sex within 3 months of donating. Some argue that this decision is to reduce the risk of transmitting recently acquired infections. While others believe that it is preventing otherwise eligible people from donating. Nonetheless, the UK are one of the most forwarding thinking countries in this sense and are constantly reviewing their blood donation processes.
10-20 minutes. It only takes 10-20 minutes to give blood. That’s less than an episode on Netflix or the time it takes for some sequencers to perform DNA sequencing. But that’s the time it takes to save a life. A life that could one day be yours.
Like everything, our blood is heavily influenced by our genetics. Therefore, ongoing efforts to refine our knowledge of how blood impacts our health are critical. This has become particularly clear with the COVID-19 pandemic, where disproportionate effects are seen across different groups.
Our blood is home to the cells of life and the infections that try to make it their home. We go throughout life trying to find treatments for different diseases whilst ensuring that they are increasingly targeted. However, we often forget a simple thing that is critical to life. Blood.
Image credit: By macrovector – www.freepik.com