What does the "N" suffix in DNA HLA allele nomenclature indicate?

The "N" suffix in DNA HLA allele nomenclature signifies that mutations may prevent the expression of certain HLA alleles. This is important in the context of histocompatibility and transplantation because the expression of HLA molecules is critical for the immune response. When an allele is marked with an "N," it indicates that while the allele may be identified at the molecular level, the resulting protein may not be produced due to genetic changes that affect its expression. This can influence matching and compatibility assessments during organ transplantation, as the presence of an HLA allele does not guarantee that it will function normally in presenting antigens.

The other choices, while discussing aspects of HLA typing and expression, do not accurately describe the significance of the "N" suffix. For instance, the notion that some alleles are not typeable by molecular or serological methods pertains to other classifications and does not specifically associate with the implications of the "N" suffix.