Chapter 8 Concepts Flashcards
How many RBC antigens are formally recognized internationally?
300 RBC antigens
Blood group antigens are defined by (structure-wise):
Carbohydrates (sugars) attached to the glycoprotein or glycolipid structures or by amino acids on a protein
Lewis, P, and I carbohydrate antigen blood groups
(like ABO and H) are not encoded by their genes but rather their genes encode specific GLYCOSYLTRANSFERASES that in turn synthesize the carbohydrate epitopes
How do Lewis, P, and I carbohydrate blood groups synthesize the carboyhydrate epitopes?
By sequential addition of sugars to a precursor
MNS, Duffy, Kell, and Kidd antigen blood groups
Significant in routine transfusion medicine and antibodies to these antigens are MORE COMMONLY encountered
A blood group system is one or more antigens produces by alleles at a single gene locus or at loci so closely linked that:
crossing over does not occur or is very rare
Most blood group genes are located on the autosomal chromosomes and demonstrate:
Straightforward Mendelian inheritance
Most blood group alleles are _____ and express a corresponding antigen.
Codominant (For example, a person who inherits alleles K and k expresses both K and k antigens on their RBCs. Some genes code for more than one antigen - i.e. the glycophorin B structure, which carries S and s antigen, also carries the U antigen)
Allele
One of two or more different genes that may occupy a specific locus on a chromosome
Silent, or amorphic, alleles exist that make:
no antigen but they are rare
When paired chromosomes carry the same silent (amorphic) allele:
a null phenotype results which can be very helpful when evaluating antibodies to unknown high-prevalence antigens
(For example, an antibody reacting with all test cells except those with the phenotype Lu(a-b-) may be directed against an antigen in the Lutheran System.
In some blood group systems, the null phenotype results in RBC abnormalities.
Some blood group systems have regulator or modifying genes, which alter:
antigen expression
These are not necessarily located at the same locus as the blood group genes they affect and may segregate independently.
(For example, RBCs with the dominant type of Lu(a-b-) have suppressed expression of all antigens in the Lutheran blood group system as well as many other antigens, including P1 and i)
Therefore, this modifying gene is inherited independently of the genes coding for Lutheran, P1, and i antigens.
Blood group antigens are detected by alloantibodies which occur:
Allo- Prefix indicating differences within a species (e.g., an alloantibody is produced in one individual against the red blood cell antigens of another individual)
Naturally (i.e., without a known immune stimulus) or as a response by the immune system after exposure to non-self RBC antigens introduced by blood transfusion or pregnancy.
Phenotype Nomenclature:
For letter antigens, a plus sign or a minus sign written on the same line as the antigen is used to designate that the antigen is present or absent
Phenotype Nomenclature Continued
For antigens that have superscripts, the letter of the superscript is placed in parentheses on the same line as the letter defining the antigen - for example Fy(a+) and Jk(a-)
For antithetical antigens, both results are written within the parentheses - Fy(a-b+)
Serologic tests:
determine only RBC phenotype NOT
genotype
A genotype is composed of the actual genes that an individual has inherited and can be determined by family or DNA studies
Sometimes the genotype can be inferred by the phenotype (probably interpretation)
