Covers the Rhesus blood group system, starting with its discovery and how its protein antigens differ from the sugar-based ABO system. It then explains the two linked genes RHD and RHCE, the RhD negative state, and why anti-RhD antibodies form only after exposure. The note also covers the risk of haemolytic disease of the newborn in pregnancy, how it is monitored and prevented, and four mnemonics, one for each main comparison.
Inside: 2 sections · 10 flashcards · 8 min
Topic 60 of 105 in the MU Sofia syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 2 sections, about 1,177 words (8 min of reading), with 10 flashcards.
In this note
Rhesus blood groups.
MNEMONIC
Rhesus blood groups.
Discovery of the Rhesus Blood Group System
In the late 1930s, doctors observed that some patients experienced dangerous reactions to blood transfusions even when their ABO blood types were compatible.
The cause was traced to a separate antigen found on the red blood cells of about 85 percent of Europeans.
This antigen resembled one found in rhesus monkeys, leading to its naming. However, the original antigen identified by Landsteiner and Wiener was later renamed "LW" by Levine to honor their contributions.
How the Rhesus System Differs from the ABO System
The ABO system is based on sugar molecules (oligosaccharides) attached to lipids or proteins on red blood cell surfaces.
In contrast, the Rhesus antigens are actual protein structures that are part of the cell membrane itself.
These proteins are produced directly by specific genes rather than being modifications of other molecules.
The Genetic Basis of the Rhesus System
The Rhesus blood group system is controlled by two closely related genes: RHD and RHCE.
These genes likely evolved from a duplication event in evolutionary history.
Each gene has different alleles. For RHD, the dominant allele is D and the absence of D is recessive. For RHCE, the different forms are C, c, E, and e.
The RHD gene produces the D protein, which is the primary cause of immune reactions in the Rhesus system.
The RHCE gene produces both the C and E proteins, using a process called alternative splicing.
All Rh proteins have similar shapes and are embedded within the red blood cell membrane, looping back and forth to form six external loops.
Understanding Rh Negative Individuals
People who do not produce the D protein are considered RhD negative.
This occurs because they inherited two copies of a non-functional or deleted RHD gene.
Their immune systems recognize the D protein as foreign if exposed to it, leading to the production of antibodies.
These antibodies specifically target the outer loops of the D protein, particularly loops three, four, and six.
Role of Rh Proteins in the Body
Rh proteins help maintain the structural integrity of red blood cells.
In rare situations where a person lacks both RHD and RHCE genes, they can suffer from a form of hemolytic anemia, where red blood cells are destroyed faster than they are made.
Other similar proteins in different blood group systems perform related roles in red blood cell function.
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