Phenotyping for HLA class II antigens requires B lymphocytes because they express HLA class II antigens. Why is this the correct basis for phenotyping?

Phenotyping for HLA class II antigens requires B lymphocytes because they express HLA class II antigens. Why is this the correct basis for phenotyping?

• A. B lymphocytes do not express HLA class I antigens.
• B. B lymphocytes express HLA class II antigens.
• C. B lymphocytes represent the majority of lymphocytes in the peripheral blood.
• D. B lymphocytes are exquisitely sensitive to complement-mediated lysis.

Answer: (B)

Phenotyping HLA class II antigens works only if the cells you test actually display those molecules on their surface. B lymphocytes are professional antigen-presenting cells and naturally express high levels of HLA class II molecules on their surface, making them the ideal cells to probe for class II types. This abundant, stable expression provides reliable detection with antibodies used in serologic or flow-based typing, enabling accurate determination of which HLA class II alleles are present. The other points don’t fit because HLA class II is not tied to a lack of class I expression in B cells (B cells do have HLA class I as well, and that isn’t the basis for class II phenotyping), the fact that B cells are a minority among peripheral blood lymphocytes isn’t relevant to why they’re used, and sensitivity to complement-mediated lysis isn’t involved in the rationale for selecting cells for class II typing.

Phenotyping HLA class II antigens works only if the cells you test actually display those molecules on their surface. B lymphocytes are professional antigen-presenting cells and naturally express high levels of HLA class II molecules on their surface, making them the ideal cells to probe for class II types. This abundant, stable expression provides reliable detection with antibodies used in serologic or flow-based typing, enabling accurate determination of which HLA class II alleles are present.

The other points don’t fit because HLA class II is not tied to a lack of class I expression in B cells (B cells do have HLA class I as well, and that isn’t the basis for class II phenotyping), the fact that B cells are a minority among peripheral blood lymphocytes isn’t relevant to why they’re used, and sensitivity to complement-mediated lysis isn’t involved in the rationale for selecting cells for class II typing.