What is the ABO Blood Group System? Who Discovered It, and Why Is It So Important in Blood Transfusion?🔗

Zoom in if the image is unclear.

The ABO Blood Group System is a method for classifying human blood based on the presence or absence of A and B antigens on the surface of red blood cells (RBCs). It was discovered by Karl Landsteiner in 1901, earning him the Nobel Prize in 1930.

Why It's Crucial for Blood Transfusion:

The ABO system is a linchpin in transfusions because mismatched blood can trigger deadly reactions. Naturally occurring antibodies (called isoagglutinins) in a person's plasma target antigens their RBCs lack:

• Group A: Has A antigens, anti-B antibodies.
• Group B: Has B antigens, anti-A antibodies.
• Group O: No A or B antigens, both anti-A and anti-B antibodies.
• Group AB: Both A and B antigens, no antibodies.

If incompatible blood is transfused (e.g., Group A blood into a Group B person), the recipient's antibodies attack the donor RBCs, causing them to burst (hemolysis). This acute hemolytic transfusion reaction can lead to shock, kidney failure, or even disseminated intravascular coagulation (DIC)—a clotting nightmare. Matching ABO types prevents this chaos, making the system vital for safe transfusions.

Zoom in if the image is unclear.

---

What Roles Do Antigens and Antibodies Play in the ABO Blood Group System? When and How Are These Antibodies Formed?🔗

• Antigens: These are protein-based molecules (specifically glycoproteins and glycolipids) on RBC surfaces. A and B antigens build on a base structure called the H antigen:

  • A Antigen: H antigen plus N-acetylglucosamine.
  • B Antigen: H antigen plus D-galactose.
  • O Group: Just the H antigen, unmodified (no A or B added due to missing enzymes).

• Antibodies: Found in plasma, these proteins (mostly IgM, sometimes IgG) are part of the body's natural defenses. In the ABO system, anti-A and anti-B antibodies form in people lacking the corresponding antigen on their RBCs—e.g., Group A folks have anti-B, Group O has both.

Formation of Antibodies:

Unlike many immune responses, these antibodies aren't triggered by blood exposure. They develop naturally in the first few years of life (detectable by 3-6 months) due to contact with environmental substances—like food, bacteria, or viruses—that mimic A or B antigens. For example, anti-A might arise from reacting to Influenza virus epitopes resembling A antigen's sugar structure. This pre-existing immunity is why ABO mismatches are so risky—they're primed to fight.

Zoom in if the image is unclear.

---

Explain the Genetics of the ABO Blood Group System in Detail. What Are the Different Genotypes and Phenotypes?🔗

The ABO blood type is controlled by a single gene, the ABO gene, on chromosome 9. It has three main alleles: I^A, I^B, and i.

• I^A: Codes for the A antigen.
• I^B: Codes for the B antigen.
• i: Produces no functional antigen (just H remains).

Inheritance Rules:

• I sup A /sup and I sup B /sup are dominant over i.

*I sup A /sup and I sup B/ sup are co-dominant with each other, both express if present together.

Genotypes and Phenotypes:

You inherit one allele from each parent, yielding six possible genotypes and four phenotypes:

• Group A:

Genotypes: IAIA or IAi. Phenotype: A antigen on RBCs.

• Group B:

Genotypes: IBIB or IBi Phenotype: B antigen on RBCs.

• Group AB:

  • Genotype: I^AI^B
  • Phenotype: Both A and B antigens.

• Group O:

  • Genotype: ii
  • Phenotype: No A or B antigens (just H).

This Mendelian dance dictates your blood type—and your transfusion fate.

Zoom in if the image is unclear.

---

What Is the Bombay Blood Group? How Does It Differ from the ABO System, and What Is Its Genetics?🔗

The Bombay Blood Group (also called hh or Oh phenotype) is an ultra-rare blood type, first identified in 1952 by Dr. Y. M. Bhende in Bombay (Mumbai).

Difference from ABO:

• In the ABO system, the H antigen is the foundation for A and B antigens. Bombay folks lack H entirely due to a defective gene, so even if they carry I^A or I^B alleles, no A or B antigens form.
• Their serum has anti-H antibodies, which attack H antigens on all ABO blood types (A, B, AB, and O)—making them incompatible with everyone except other Bombay types.

Genetics:

• Controlled by the H gene (FUT1), which codes for a fucosyltransferase enzyme that adds a sugar to form the H antigen.
• Bombay phenotype arises from inheriting two recessive hh alleles, rendering the enzyme useless—no H, no A, no B.
• It's a separate layer from the ABO gene; someone can be genetically I^AI^A but still Bombay (hh), showing no antigens.

Zoom in if the image is unclear.

---

What Challenges Does the Bombay Blood Group Pose for Blood Transfusion? What Is the Para-Bombay Phenotype?🔗

Transfusion Challenges:

• Bombay individuals can only receive blood from other Bombay donors. Their anti-H antibodies reject all ABO types (even O, the "universal donor"), risking severe hemolytic reactions if mismatched.
• Rarity compounds the issue: about 1 in 10,000 in India, 1 in a million in Europe. Finding a donor is a needle-in-a-haystack ordeal.

Para-Bombay Phenotype:

• An even rarer twist, where RBCs lack ABH antigens, but some H (or A/B) antigens appear in secretions (like saliva).
• Genetics: Caused by a partial FUT1 mutation, with a working FUT2 gene (controls secretion antigens).
• Transfusion: They're still treated like Bombay—only Bombay blood works—since their RBCs lack H, and anti-H antibodies may still lurk.

Both types are transfusion headaches, demanding exact matches in a world where they're almost mythical.

---

Zoom in if the image is unclear.

---