The H antigen is found in lowest concentration on which phenotype of red blood cells?

The H antigen is found in lowest concentration on which phenotype of red blood cells?

• A. Group B
• B. Group A1B
• C. Group A2B
• D. Group O

Answer: (C)

H antigen is the starting structure for ABO antigens; it acts as the substrate that glycosyltransferases convert into A or B antigens. The amount of H antigen on red cells therefore inversely tracks how much A or B antigen is present: the more A and/or B antigen expressed, the less H antigen remains. In O cells, there’s no A or B activity, so H stays abundant. In cells that make A or B, H is reduced as it’s modified into those antigens. When a cell carries both A and B antigens (the AB phenotype), a large portion of H has been converted, leaving only a small residual H. Within AB subtypes, the A2 variant has weaker A antigen expression than A1, but the presence of B antigen still uses up H. The combination of both A and B activities in A2B leads to the greatest overall consumption of H, producing the lowest residual H antigen among the given phenotypes. So, the red cells with the least H antigen are those of the A2B phenotype because both glycosyltransferase activities are present, converting more H into A and B antigens.

H antigen is the starting structure for ABO antigens; it acts as the substrate that glycosyltransferases convert into A or B antigens. The amount of H antigen on red cells therefore inversely tracks how much A or B antigen is present: the more A and/or B antigen expressed, the less H antigen remains.

In O cells, there’s no A or B activity, so H stays abundant. In cells that make A or B, H is reduced as it’s modified into those antigens. When a cell carries both A and B antigens (the AB phenotype), a large portion of H has been converted, leaving only a small residual H. Within AB subtypes, the A2 variant has weaker A antigen expression than A1, but the presence of B antigen still uses up H. The combination of both A and B activities in A2B leads to the greatest overall consumption of H, producing the lowest residual H antigen among the given phenotypes.

So, the red cells with the least H antigen are those of the A2B phenotype because both glycosyltransferase activities are present, converting more H into A and B antigens.