Which system is composed of antigens found primarily in saliva and plasma?

Which system is composed of antigens found primarily in saliva and plasma?

• A. Lewis
• B. ABO
• C. Rh
• D. Kell

Answer: (A)

The Lewis system is defined by soluble antigen determinants (Le^a and Le^b) that are produced in secretory tissues and found in body fluids such as saliva and plasma. Red cells can acquire these antigens by adsorption from the surrounding plasma, so the observed Lewis expression on RBCs reflects soluble antigens present in secretions and plasma rather than intrinsic membrane components. In contrast, the ABO, Rh, and Kell systems are based on antigens that are built into the red cell membrane itself, not primarily found in saliva or plasma. This is why Lewis is the system described as having antigens found mainly in saliva and plasma.

The Lewis system is defined by soluble antigen determinants (Le^a and Le^b) that are produced in secretory tissues and found in body fluids such as saliva and plasma. Red cells can acquire these antigens by adsorption from the surrounding plasma, so the observed Lewis expression on RBCs reflects soluble antigens present in secretions and plasma rather than intrinsic membrane components. In contrast, the ABO, Rh, and Kell systems are based on antigens that are built into the red cell membrane itself, not primarily found in saliva or plasma. This is why Lewis is the system described as having antigens found mainly in saliva and plasma.