3.07 Blood Type Origins Flashcards
Concept wherein a certain gene has many alleles across the population
polymorphism
Where many genes encode for the same phenotype
polygeny
Inheritance pattern wherein the offspring expresses both sets of genes from parents
co-dominance
The basic mechanism on how the blood system works (key terms: antibodies, antigens)
Antibodies bind to antigens on foreign RBCs marking them for the extermination of the immune system (activates the complement cascade)
Serves as the precursor for other ABO blood types
H antigen
The four monosaccharide rings that compose the precursor for the ABO blood types
galactose, N-acetylglucosamine, another galactose and fucose
The H antigen is completed by the enzyme __
fucosyltransferase
Fucosyltransferase is encoded by the __ gene on chromosome 19, and it evidently adds the monosaccharide __.
FUT1; 19; fucose (4th)
The ABO locus is located in which chromosome?
chromosome 9
The blood type of a person is dictated by this general mechanism of antigen synthesis (three-step mechanism)
allele –> enzyme –> monosaccharide
What are the corresponding enzymes and monosaccharides responsible for the four blood types?
A - alpha-1,3-N-acetylegalactosamine transferase - H antigen + GlcNac
B - alpha-1,3-galactosyl transferase - H antigen + Gal
O - NO enzyme - nothing added to H antigen
What causes the lack of an enzyme for the O antigen?
Deletion of guanine at position 261 of exon 6
Inactive counterpart of the H allele
h
What does having a homozygous h/h do to a person?
It removes the ability to produce the enzyme fucosyltranferase, thereby rendering the H antigen incomplete. It makes it difficult for them to receive blood through transfusion because their bodies will recognize non-homozygous h blood types as foreign.
What do you call the phenotype for homozygous h individuals?
Bombay phenotype
T/F. ABO antigens are either membrane-bound or free form.
True
If the antigens are membrane-bound, they can either be attached to __ or __ of RBCs.
glycoproteins; glycolipids
T/F. Saliva can always be used as a substitute for blood typing because ABO antigens can also be found in secretions.
False. Not everyone is a secretor, or those whose ABO antigens exist in water-soluble forms
The ABO antigens may exist in free form and manifest themselves in bodily secretions except __
Cerebrospinal fluid
T/F. There is no correlation between ABO phenotype and blood clotting.
False. Blood group O have 25% less FVIII and vWF in their plasma
How many known antigens are there for the Rh blood group system? What are the five most important?
49; D, C, c, E, e
What does having the Rh factor imply?
Having the D antigen; not having the Rh factor (negative) means you don’t have the D antigen
The antigens involved in the Rh blood group system are __ while those of the ABO system are __.
proteins; oligosaccharides
Two genes that encode for the Rh blood type. They are located in chromosome __.
RHD and RHCE; chromosome 1
How does the D/d polymorphism arise?
Through a deletion of the entire RHD gene
The C/c polymorphism arises from what?
Four SNPs in the RHCE gene, one of which determines the C or c antigen specificity
How does the E/e polymorphism arise?
Single SNP in the RHCE gene
T/F. RHCE protein is a transmembrane multipass protein while RHD isn’t.
False. They are both transmembrane multipass proteins.
T/F. Rh proteins are not glycosylated.
True.
What are the functions of the Rh proteins?
Maintenance of membrane integrity - loss of which may cause mild hemolytic anemia
Involved in the transport of ammonium across the RBC membrane
Hemolysis in Rh incompatibility is (intra-/extra-)vascular.
extravascular
What is the severity of having: Anti-D antibodies? Anti-c antibodies? Anti-C antibodies? Anti-E antibodies? Anti-e antibodies?
Anti-D and -c can cause severe diseases
Anti-C, -E, and -e can cause mild to moderate disease.
T/F. Blood antigens can only be found in RBCs.
False. HLAs.
Loci of HLA
Chromosome 6
HLA genes are divided into:
Class I (HLA A, B, C) and Class II (HLA DP, DM, DOA, DOB, DQ, DR)
T/F. HLA genes are polymorphic, polygenic, and co-dominant.
True.
Class of MHC that presents peptide remnants to cytotoxic T cells; those recognized as foreign will be induced to apoptose.
Class I
Class of MHC that binds peptides derived from extracellular proteins, peptides are presented to helper T cells
Class II
Happens when T cells bind to non-self MHCs
Cross-reactivity
Two ways that cross-reactivity occurs
Peptide-dominant binding
MHC-dominant binding
T/F. GVHD is when the body rejects the transplanted tissue.
GVHD happens when the transplanted tissue is the one that rejects the body itself.
Testing used to know the histocompatibility of transplants. It uses sera that contain specific antibodies to HLA antigens.
Serologic Testing
