GENERAL Y VARIABLES MACROECONÓMICAS EN MÉXICO, 1960-2019
MATERIALES Y MÉTODOS
producing A antigen, (shown in this diagram) or
4. B gene causes D-galactose to be added to H substance, producing B antigen.
5. If both A and B genes present, some H-chains converted to A antigen, some converted to B antigen.
6. If H gene absent (extremely rare), no H substance can be formed, and therefore no A or B antigen. Result is Bombay blood group.
Bombay blood group
Bombay blood group lacks H gene and therefore cannot make H antigen (H substance).
Since the H substance is the precursor for the A and B antigens, these antigens also are not made. The cells type as O and the serum has anti-A, anti-B, and anti-H since the individual lacks all of these antigens. Anti-H agglutinates O cells. The only cells Bombay individuals do not agglutinate are from other Bombay blood people since they lack H antigen,
Bombay phenotype
H antigen is not expressed on RBCs.
H antigen is not found in saliva.
Serum contains anti-H.
Genotype: h/h se/se
Para-Bombay phenotype
H antigen is weakly expressed on RBCs.
H antigen may be present or absent in saliva.
Serum contains anti-H.
Genotype: (H), Se/Se or Se/se or se/se
Subgroups of A and B
The subgroups of A and B are caused by decreased amounts of antigen on red cells.
The most common are subgroups of A. Approximately 80%
of the A's and AB's have a normal expression of A1. Most of the other 20% are either A2 or A2B. This subgroup has fewer H chains converted to A antigen – result is more H chains on red cell, and fewer A antigens.
There are other, weaker subgroups of A exist: A3; Aint; Am, Ax; Ael. Each has a different pattern of reacting with anti-A, anti-A, and various antibody-like substances called lectins.
Lectins are extracts of seeds of plants that react specifically with certain antigens.
Ulex europaeus, or lectin H, which agglutinates cells that have H substance.
Dolichos biflouros, or lectin A1, which agglutinates cells with A1.
Lectin-H reacts strongest with O cells, which has a high concentration of H antigen, and weakest with A1 cells, which have a low concentration of H.
Lectin O cells A2 cells A2B cells B cells A1 cells A1B cells Bombay cells
Lectin-H 4+ 3+ 2-3+ 2+ 1+ / 0 1+ / 0 0
Lectin-A1 0 0 0 0 4+ 4+ 0
Differentiating Subgroups of A
1. Use lectin-A1 to differentiate A1 cells from all others - will agglutinate only A1 cells 2. Look for weaker or mixed field reactions
3. Look for anti-A1 in serum (serum reacts with A1 cells but not A2 cells) 4. Look at strength of reactions with anti-A,B or with lectin-H
GROUP A1 A2 A3 Ax
Reaction with anti-A 4+ 4+ mf 0
Reaction with anti-A,B 4+ 4+ mf 2+
Reaction with Lectin-A1 4+ 0 0 0
Reaction with Lectin-H 0-w 1-2+ 2+ 2-3+
Presence of anti-A1 no may may often in serum
Problems with Ax:
Because Ax cells initially type as O and serum usually has anti-A1, (along with anti-B), patient forwards and reverses as O. Unfortunately when Ax is transfused into an O individual, the naturally occurring anti-A,B will react with the donor cells causing a transfusion reaction.
Therefore: To prevent Ax from being erroneously typed as O, confirm all group O donors with anti-A,B.
Rh SYSTEM Rh Antigens
D (Rh) is the most important antigen after A and B antigens. Unlike the anti-A and anti-B antibodies, anti-D antibodies are only seen if a patient lacking D antigen is exposed to D+
cells. The exposure of D+ cells usually occurs through pregnancy or transfusion.
There are at over 50 Rh antigens that have been identified including those that are either combinations of these antigens or weak expressions of the above antigens, but most Rh problems are due to D, C, E, c or e.
Characteristics of Rh antigens
The Rh antigens together are proteins of 417 amino acids. These proteins cross the red cell membrane 12 times. There are only small loops of the protein on the exterior of the cell membrane.
Therefore Rh antigens are not as available to react with their specific antibodies and there are fewer antigen sites than ABO. Unlike the ABO system, Rh antigens are not soluble and are not expressed on tissues. They are well developed at birth and therefore can easily cause hemolytic disease of the newborn if the baby has a Rh antigen that the mother lacks.
Besides the antigens being well-developed at birth, they are very good immunogens. This is especially true to D, which if the most immunogenic after A and B antigens.
Rh Antibodies
Unlike the ABO antibodies that are mainly IgM, Rh antibodies are commonly IgG. They are NOT naturally occurring and therefore are formed by immune stimulus due to transfusions or baby's red blood cells during pregnancy. The most common antibody to form is anti-D in Rh negative individuals.
Since Rh antibodies are IgG they bind best at 37oC and their reactions will be observed with indirect antiglobulin technique. Agglutination reactions are enhanced by high protein (albumin), low-ionic strength saline (LISS), proteolytic enzymes (papain) and polytheylene glycol (PEG).
Rh antibodies will react more strongly with homozygous cells than with heterozygous cells.
For example, an anti-E will react with strongly with E+E+ cells and more weakly with E+e+
cells. This is called dosage effect.
Both Hemolytic Disease of the Newborn and Hemolytic Transfusion Reactions can occur due the various Rh antibodies. Anti-D is the most common cause of hemolytic disease of the newborn. Since D antigen is so immunogenic we screen all donor units for the D antigen.
Therefore if an individual is A+, it means both the A and the D antigens are present. On the other hand, if an individual is A-, the A antigen is present and the D antigen is absent.
To prevent problems due to anti-D:
always give Rh-negative individuals Rh-negative blood
give Rhimmune globulin to Rh-negative mothers to prevent formation of anti-D during pregnancy.
The incidence of Rh antibodies
Anti-D most common antibody seen in Rh(D) negative people
Anti-E most common antibody seen in Rh pos people since only 30% of population have the antigen
Anti-C or Anti-c less common - most people have the antigen
Anti-e often seen as autoantibody and will make it difficult to find compatible blood since 98% of the population have the e antigen
Anti-C,e or Anti-c,E often seen in combination. If a patient lacks both a C and e and has made an anti-C, then enhancement techniques should be done to make sure that an anti-e is not also present.
Rh System Inheritance
Fisher-Race theory involved the presence of 3 separate genes D, C, and E and their alleles c and e and the absence of D since an anti-d has never been found. These three genes are closely linked on the same chromosome and are inherited as a group of 3. The most
common group of 3 genes inherited is CDe and ced is the second most common.
Weiner Theory
Weiner believed there was one gene complex with a number of alleles resulting in the presence of various Rh antigens. According to Weiner there were 8 alleles, R, R1, R2, Rz, r, r', r", ry , which ended up with different antigens on the red cells that he called Rh, rh', rh", hr', hr". If a person has the Fisher-Race genotype of DCe/DCe, it is easier to refer to that type as R1R1 Tippett Theory
Tippett predicted that there are two closely-linked genes - RHD and RHCE. The RHD gene determines whether the D antigen that spans the membrane is present. Caucasians who are D negative have no gene at that gene loci.
The RHCE gene determines C, c, E, e antigens produced from the alleles:
RHCe
RHCE
RHcE
RHce
Rh Gene Complexes, Antigens, Possible Combinations and Percentages
Haplotypes Genes Present Antigens Present Phenotype Percentage
R1 RHD RHCe D,C,e R1 42%
r RHce dce r 37%
R2 RHD RHcE DcE R2 14%
R RHD RHce Dce R 4%
r' RHCe dCe r' 2%
r" RHcE dcE r" 1%
Rz RHD RHCE DCE Rz <1%
ry RHCE dCE ry <1%
Translating From Wiener To Fisher-Race
1. R always refers to D whether it is R, R1, R2, or the very rare Rz. 2. r always refers t the lack of D
3. o refers to having no C or E 4. 1 or ' always refers to C 5. 2 or " always refers to E
6. The very rare haplotypes that have both a C and E are given letters from the end of the alphabet z and y.
Determining Genotypes From Phenotypes
The following steps will be helpful in determining from the individual's phenotype. These rules are based on probability so the least likely genotypes will involve Rz or ry.
1. Type patient for the five Rh antigens: D, C, c, E, e 2. Start with D: is it positive or negative?
1. If negative, the individual will be homozygous d.
2. If positive for D, you can't tell yet whether the individual is homozygous or heterozygous for D. Therefore, put D on just one chromosome.
3. Look at C: is it positive or negative?
1. If negative, put c on each chromosome.
2. If positive, look at c result to determine if the C is homozygous or heterozygous.
If there is no c present, there would be two C and it would be homozygous.
If a c is present as well as C, they are heterozygous.
3. If homozygous, then put C on each chromosome.
4. If heterozygous, put C on same chromosome as D; put c on other.
4. Look at E: is it positive or negative?
1. If negative, put e on each chromosome.
2. If positive, look at e result to determine if homozygous or heterozygous.
3. If homozygous, put E on each chromosome.
4. If heterozygous, put E on same chromosome as the D unless the D already has a C; put e on other chromosome. DCe is more common than DcE and DCE is extremely rare.
5. Put C and E together on same chromosome only if no other possible combinations
Most Common Genotypes
The following genotypes are listed as the most common with 1 being the most common in Whites and 7 the least common. Rz and ry are so rare they are not included.
Incidence of the most common genotypes
Antigens Present Genotype Incidence(%)
DCE Weiner Haplotypes Whites Blacks
1 D, C, c, e DCe/ce R1r 31.1 8.8
Paternity testing of blood group antigens is based on a process of exclusion. Since the RHD and RHCE are closely linked and Ce, ce, cE are produced by a single gene, there are limited combinations that the father can provide.
HDN predictability by testing father's Rh genotype. This helps predict likelihood of HDN due to D when mom has anti-D. The most common Rh genotype of father will indicate whether baby has O%, 50%, or 100% probability of being D positive.
If the father is also D negative (ce/ce), the baby will be D negative as well and there is a 0% probability of the baby suffering from Rh HDN.
If the father's Rh genotype appears to be either, R1r, R2r or Ror, the baby has a 50%
probability of being D positive and suffering from Rho HDN.
On the other hand if a father's Rh genotype appears to be any of the following, R1R1, R2R2, R1R2, RoRo, R1Ro, or R2Ro, the baby has a 100% probably of getting a D gene from his father and therefore being D positive and suffering from Rh HDN.
Variants Weak D (Du)
Weak D is a weakly expressed D antigen that will only be demonstrated after incubation at 35-37oC followed with antiglobulin testing. (ie being demonstrated only by Coombs
technique). An Rh control must always be run along with the weak D test. Always consult the product insert to determine if Rh Control needs to be run when performing the immediate spin D testing. The following results could be obtained when performing the D testing:
Immediate Spin 37oC Anti-D AGT
Interpretation Anti-D Rh Co Anti-D Rh Co Anti-D Rh Co
+ 0 D positive
0 0 0 0 + 0 Weak D
0 0 0 0 0 0 True D negative
0 0 0 0 + +
Or any time the Rh control is positive, you cannot interpret
results and need to perform further testing
Testing for Weak D
AABB requires that all donor blood that originally fails to react with anti-D at immediate spin must be tested for weak D. Units that test weak D positive would be labeled D positive and would be transfused only to D positive individuals.
Hospitals may or may not test all Rh negative recipients for weak D. The cost of time and reagents is minimized if only the immediate spin. This may create some confusion with the recipient if their donor card indicates they are Rh positive but they type Rh negative when they are the recipient. Recipients that type D negative at immediate spin would be given D negative blood, which not create a problem for the patient.
When performing testing prenatal and postnatal mothers, D-negative blood at immediate spin would be tested for weak D as well to determine if they are eligible for Rh Immune Globulin. Since Rh Immune Globulin is actually anti-D it is safe for a true D negative, but not for a weak D positive mother.
Why do weak D's exist?
Quantitative Weak D There are individuals that quantitatively produce fewer D
antigen sites. This is more common in Blacks and is often seen with the Dce haplotype.
On rare occasions among Whites an unusual DCe or DcE may also produce a quantitatively decrease weak D.
Position Effect Weak D In this case the D is weakened by the position of a C on the opposite haplotype which is called the trans position. The two Rh genotype
combinations where this type of weak D is seen are: Dce/Ce and DcE/Ce. Today this type of weak D would type as a regular D due to the improvement of reagents.
Partial D antigen (Mosaic D) It has been found that some D-positive individuals make an alloanti-D that reacts with other D positive cells but not their own. Many of these will demonstrate a weak D type of reaction. In this type of weak D, the individuals are lack some of the components of the D antigen and therefore are able to make allantibodies to those specific components if they are transfused with D positive blood.
Other Rh System Variants
There are presently 46 Rh antigens identified and named. The following are the most common of those variants
Cw is a low frequency antigen found in approximately 2% of Whites and 1% of Blacks.
It is not an allele of C and c. Its allele is MAR, which is found in 99.9% of the population.
V and VS are low frequency alleles found in 1% or less of the Whites, but are more common in Blacks. V is found in 30% of the Blacks and VS in 32%.
G is present when D or C present due to the present of serine at the 103 position of the Rh polypeptide. Anti-G will react with both D+ and C+ cells.
f is present when c and e together on same chromosome: Dce or ce. This is the most common of what are called cis product antigens.
Rhnull has no Rh antigens on their red cells but these individual can transmit normal Rh antigens to their offspring. In the most common type the core Rh polypeptide is missing. A less common type has the regulator gene that turns off the expression of Rh.
There have been at least 43 individuals in 14 families that are Rhnull. In these individuals the red blood cell membrane is abnormal and some of these have been identified when it was observed that they had hemolytic anemia and abnormal red cell morphology. If these individuals develop an Rh antibody following a transfusion or pregnancy, it is considered a anti-total Rh antibody.
Rh Typing False Positives
1. When following through to AGT for weak D and will be identified as false positive by a positive Rh control. This is seen when a patient/donor has strong positive DAT. The cells are coated with antibody (not necessarily Rh antibody) in vivo. Albumin is necessary in reagent Anti-D to overcome the zeta potential allowing cells coated with IgG Anti-D to get close enough together to agglutinate, but cells coated in vivo with any IgG antibody will also agglutinate in albumin.
These false positives are corrected by using form of Anti-D that does not require albumin. There are two types of alternative types of anti-D:
Monoclonal (IgM) anti-D will cause agglutination of D positive cells without the presence of albumin at room temperature. A number of facilities normally use this type of anti-D and therefore do not routinely use Rh control.
Chemically modified anti-D has been modified by breaking the disulfide bonds closest to the hinge region so antibody can reach cells that are farther apart.
2. False positive can also be caused by rouleaux formation, which will look like
agglutination macroscopically. Rouleaux would be identified microscopically due to the "coin-stacking" appearance of the red cells. This false positive would be
corrected by washing cells 3 to 4 times and then retesting.
False Negatives
False negatives are not readily identifiable, but can occur in the following instances:
The most common is the result of too heavy cell suspension due to too many cells for the amount of antibody in the antisera.
They may also rarely be caused by extremely strong positive DAT. In this case a the patient's D antigen sites are coated in vivo and there are no sites left for commercial anti-D to attach to. This can be fixed by heating cells gently to elute off antibody without damaging cells, then re-test.