Blood Groups and Disease Association: How Antigens Affect Susceptibility

Ask most people what their blood group means, and they will mention transfusions or maybe pregnancy compatibility. But the antigens sitting on the surface of your red blood cells do a lot more than decide who can donate blood to whom. They are molecular flags that pathogens, parasites, and even your own immune system react to. Over the last few decades, researchers have found that these tiny surface markers are linked to everything from malaria resistance to heart disease risk. Here is what the evidence actually shows, and where it is still uncertain.

Why blood group antigens are more than a transfusion label 🔗

Blood group antigens are sugar or protein structures attached to the membrane of red blood cells. The ABO and Rh systems are the most familiar, but scientists have catalogued dozens of blood group systems, including Duffy, Knops, Lewis, Kell, and Raph. Each of these antigens sits on a specific membrane protein that usually has its own biological job, such as transporting molecules, anchoring the cell’s structure, or interacting with the immune system.

Because these antigens change what the RBC membrane looks like from the outside, they also change how well certain bacteria, viruses, and parasites can latch onto the cell or the surrounding tissue. Some pathogens have evolved to use a specific antigen as a docking site. If you carry that antigen, you become an easier target. If you do not, you may have a natural head start against that particular infection. This is the basic logic behind almost every blood group and disease association discussed in medical genetics literature.

Secretors and non-secretors: two different immune strategies 🔗

Not everyone displays blood group antigens the same way. Around 80 percent of people are secretors, meaning they release soluble copies of their ABO and related antigens into saliva, mucus, tears, and other body fluids. The remaining group are non-secretors, whose antigens stay confined to their red blood cells and a few other tissues. This distinction is controlled by the FUT2 gene, and it changes infection risk in two opposite directions depending on the pathogen involved.

When secreted antigens act as decoys 🔗

For several bacteria, the antigens floating in mucus and saliva work like decoys. They intercept the pathogen before it ever reaches a real cell to infect. Because non-secretors lack this decoy layer, they tend to face a higher risk of infections such as those caused by Neisseria meningitidis, Haemophilus influenzae, and certain strains of E. coli, as reported in a large UK cohort study on FUT2 genotype and infection risk.

When secreted antigens become the entry point 🔗

Other pathogens exploit the same antigens as their actual attachment receptor. Norovirus, several rotavirus strains, and Helicobacter pylori specifically bind to the fucosylated antigens that secretors display on their gut and stomach lining. This means secretors are, somewhat counterintuitively, more vulnerable to these particular infections, while non-secretors show relative resistance. Studies on enterotoxigenic E. coli in Bangladeshi children found a similar pattern, where the specific antigen profile, not simply secretor status alone, determined susceptibility. The takeaway is that secretor status does not universally protect or endanger you. It reshapes your risk profile pathogen by pathogen.

ABO blood groups and infectious disease patterns 🔗

The ABO system has the largest body of research behind it, partly because it is the easiest blood group to test for and partly because roughly 100 years of studies have accumulated. The associations below are statistical patterns from population studies, not universal rules for every individual.

Blood group A 🔗

People with blood group A show higher reported associations with Hepatitis B, HIV, H. pylori, H1N1 influenza, smallpox, and Pseudomonas aeruginosa. During the COVID-19 pandemic, several hospital-based studies, including one from Sir Ganga Ram Hospital in Delhi, found blood group A patients had comparatively higher odds of testing positive than blood group O patients.

Blood group B 🔗

Blood group B has been linked with a higher likelihood of falciparum malaria, gonorrhea, tuberculosis, Hepatitis C, and infections from Streptococcus pneumoniae and Salmonella. It also appears frequently in studies on H3N2 influenza susceptibility.

Blood group O 🔗

Blood group O carries a mixed reputation. It appears protective in several contexts, including a documented reduced risk of severe malaria linked to lower rates of infected-cell clustering, but it is also associated with higher susceptibility to E. coli, Hepatitis B and C, norovirus, plague, tuberculosis, mumps, SARS, and dengue. Cholera is the clearest exception to the idea that O is always the “safe” blood group. Multiple studies, including a comprehensive review of ABO disease associations, confirm that blood group O individuals face a notably higher risk of developing severe, dehydrating cholera once infected with Vibrio cholerae.

Blood group AB 🔗

As the rarest ABO group, AB has fewer large studies behind it, but existing data connects it with HIV-2, influenza A and B, dengue haemorrhagic fever, smallpox, and infections from E. coli and Salmonella.

Malaria: the clearest case of blood group evolution 🔗

Malaria offers some of the strongest evidence anywhere in human genetics for a blood group shaping survival at a population level.

Duffy antigen and Plasmodium vivax 🔗

Plasmodium vivax, one of the parasites causing malaria, needs the Duffy antigen to invade red blood cells. People who are Duffy-negative, a trait that is extremely common across sub-Saharan Africa, lack this docking site and were long considered almost completely resistant to vivax infection. Research summarised in a study from Madagascar shows this resistance is strong but not absolute; the parasite has since found workaround pathways in some Duffy-negative populations, which is an active area of ongoing research.

Knops system and Plasmodium falciparum 🔗

The Knops blood group system, tied to the complement receptor CR1 on red blood cells, plays a role in Plasmodium falciparum malaria, the deadlier of the two major malaria species. Variants in this system affect how parasite-infected cells cluster together, a process called rosetting, which in turn influences how severe an infection becomes. A recent overview in Frontiers in Cellular and Infection Microbiology details how CR1 variants and other blood group receptors together shape falciparum malaria severity.

Rh, Lewis, and other lesser-known blood group systems 🔗

Beyond ABO and Duffy, several other blood group systems carry disease links worth knowing. The Rh system, best known for its role in haemolytic disease of the newborn, is also associated with Hepatitis B susceptibility and the tropical bacterial infection Yaws. The RHAG blood group, closely related to Rh, has been connected to chronic and autoimmune haemolytic anaemia.

The Lewis blood group system, which overlaps with secretor biology, is tied to both peptic ulcer risk and cholera susceptibility. Research on cholera patients found that people with the Le(a+b−) phenotype faced a significantly higher risk of symptomatic infection compared with the Le(a−b+) phenotype, as shown in a study published in PLOS Neglected Tropical Diseases. Meanwhile, the Raph blood group system has been linked to certain forms of renal disease, though this area has fewer large-scale studies.

Blood groups and non-communicable diseases 🔗

The associations are not limited to infections. A growing body of epidemiological work connects ABO type with several chronic, non-infectious conditions.

Heart disease and clotting disorders 🔗

Non-O blood groups, particularly A and AB, are repeatedly linked with a higher risk of myocardial infarction, venous thromboembolism, and ischemic stroke. One proposed mechanism involves higher circulating levels of von Willebrand factor and Factor VIII in non-O individuals, both of which play a role in blood clotting.

Cancer risk 🔗

Blood group A shows an elevated association with gastric, pancreatic, and nasopharyngeal cancers. Blood group B has been linked with ovarian cancer and certain lymphomas, while blood group O is associated with a higher risk of some neuroendocrine tumours and malignant melanoma. AB has shown associations with nasopharyngeal cancer as well.

Autoimmune and metabolic conditions 🔗

Blood group B is connected with type 2 diabetes and hypertension in several population studies, while AB has been linked to preeclampsia and cognitive impairment in some cohorts. On the Rh side, autoimmune haemolytic anaemia and haemolytic disease of the newborn remain the best-documented conditions.

Correlation, not proof: reading the evidence carefully 🔗

It is worth being precise about what this body of research actually establishes. Almost all of these findings come from epidemiological studies that compare disease rates across blood groups in large populations. They show statistical association, not confirmed cause and effect. A blood group can raise or lower the odds of a disease without being the direct trigger for it. Genetics, environment, diet, healthcare access, and dozens of other factors interact with these antigens in ways researchers are still mapping out.

This is why review articles consistently call for validated biological mechanisms before treating any of these associations as diagnostic or predictive on an individual level. Knowing your blood group does not tell you your fate. It tells you which end of a probability curve you sit on, for a specific pathogen or condition, based on population-level data.

What do you think? If pathogens have shaped which blood groups became common in different populations over thousands of years, what does that suggest about how modern diseases like COVID-19 or dengue might influence human genetics going forward? And should blood group ever factor into personalised healthcare decisions today, given how much these associations still rely on population averages rather than individual certainty?

References

1. https://www.ncbi.nlm.nih.gov/books/NBK100894/
2. https://pmc.ncbi.nlm.nih.gov/articles/PMC6171556/
3. https://pmc.ncbi.nlm.nih.gov/articles/PMC5587594/
4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8593001/
5. https://onlinelibrary.wiley.com/doi/10.1155/2021/6629060
6. https://www.pnas.org/doi/10.1073/pnas.0912496107
7. https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2025.1727335/full
8. https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0001413