BLOOD GROUP SYSTEMS

What are blood groups and how are they determined?

Blood groups classify blood based on antigenic substances on erythrocytes.

These antigens (proteins, carbs, glycoproteins/glycolipids) are inherited.the most clinically significant are ABO and Rh.

What determines A and B antigens in the ABO system?

Antigen A = H substance + N-acetyl-galactosamine.

Antigen B = H substance + D-galactose.

Both are glycolipids and start forming in the 3rd month of intrauterine life.

What are ABO agglutinins and their features?

They are IgM/IgG antibodies, mainly IgM.

Also called isohaemagglutinins. Do not cross placenta.

What is the Bombay phenotype?

hh genotype prevents synthesis of H antigen → no A/B antigens even if A/B genes present. Looks like group O but produces anti-H antibodies. Can only receive blood from other Bombay phenotype individuals.

ABO gene location and types of alleles?

Located on chromosome 9q34. Alleles: A, B, O. A and B are co-dominant, O is recessive. A1 > A2 > O

Describe the function of enzymes encoded by ABO genes.

A gene: adds N-acetyl-galactosamine. B gene: adds galactose. O gene: non-functional transferase due to a 261delG deletion

Clinical relevance of ABO system?

Transfusion compatibility. Organ transplantation. Paternity testing. Forensics. Anthropology. Group O: universal donor, Group AB: universal recipient

What is the secretor system in ABO?

Secretors (75%) express ABO antigens in saliva, sweat, etc. Genotype: Se/Se or Se/se. Non-secretors (25%): only on RBCs (se/se)