Study Notes: Blood Typing Principles and Genetics

Historical Context of Blood Typing

• Karl Landsteiner: Austrian physician and immunologist who discovered the $ABO$ blood groups in $1900$.

• Alexander Wiener: Collaborated with Landsteiner in $1937$ to discover the Rhesus ($Rh$) group.

• Erythrocytes: Red blood cells ($RBCs$) that determine blood type based on the presence or absence of three specific antigens: $A$, $B$, and $Rh$ factor.

Antigens and Antibodies

• Antigen: A substance such as a protein, toxin, or carbohydrate that triggers an immune response and the production of antibodies.

• Antibodies: Proteins specific to a foreign antigen (labeled "anti-X"); they bind to antigens through a process called agglutination, signaling the immune system to destroy the targeted cells.

• Natural Presence: Individuals typically possess antibodies for the $RBC$ antigens that are NOT present on their own $RBCs$.

ABO and Rh Blood Group Characteristics

• A+: Contains anti-$B$ antibodies ($35.7\%$ of U.S. population).

• A-: Contains anti-$B$ and anti-$Rh$ antibodies ($6.3\%$ of U.S. population).

• B+: Contains anti-$A$ antibodies ($8.5\%$ of U.S. population).

• B-: Contains anti-$A$ and anti-$Rh$ antibodies ($1.5\%$ of U.S. population).

• AB+: Contains no antibodies ($3.4\%$ of U.S. population).

• AB-: Contains anti-$Rh$ antibodies ($0.6\%$ of U.S. population).

• O+: Contains anti-$A$ and anti-$B$ antibodies ($37.4\%$ of U.S. population).

• O-: Contains anti-$A$, anti-$B$, and anti-$Rh$ antibodies ($6.6\%$ of U.S. population).

Clinical Importance

• Blood Transfusions: Identification is vital to prevent in vivo agglutination, which occurs if the patient's antibodies bind to transfused $RBCs$ or vice versa.

• Erythroblastosis Fetalis: Also known as hemolytic disease of the newborn; occurs when an $Rh-$ mother produces anti-$Rh$ antibodies that attack the $RBCs$ of an $Rh+$ baby.

• RhoGAM: A treatment administered to pregnant mothers to prevent hemolytic disease.

Blood Type Genetics

• Alleles: The $ABO$ group is determined by three alleles ($A$, $B$, and $O$). The $Rh$ group is determined by two alleles ($Rh+$ and $Rh-$).

• ABO Genotypes and Phenotypes:     * $A$ Type: $AA$ or $AO$     * $B$ Type: $BB$ or $BO$     * $AB$ Type: $AB$     * $O$ Type: $OO$

• Rh Genotypes and Phenotypes:     * $Rh+$ Type: $Rh+ Rh+$ or $Rh+ Rh-$     * $Rh-$ Type: $Rh- Rh-$

Questions & Discussion

• Q: Mr. Smith and Ms. Brown have a child together. What are the chances the child will be $Rh+$? What are the chances the child will be $Rh-$?

• Q: Can two type $O$ parents have children that are not type $O$? Explain.

• Q: Mr. Green and Ms. Brown have a child together. What are the chances of the child being any of the possible blood types? Assume Mr. Green is $Rh+ Rh+$.