Which of the following proteins are NOT class II gene products?

The chosen answer is correct because HLA-DD is not recognized as a class II gene product in the human major histocompatibility complex (MHC). Class II MHC molecules are primarily involved in presenting antigens to CD4+ T-helper cells and are essential for the immune response, especially against extracellular pathogens.

HLA-DP, HLA-DQ, and HLA-DR are all examples of class II MHC proteins. They play significant roles in the immune system by presenting peptide fragments derived from extracellular proteins to T-cells, activating the adaptive immune response. The presence of specific genes such as HLA-DP, HLA-DQ, and HLA-DR in the context of antigen presentation is well established in immunology, highlighting their importance in the activation of helper T-cells and the overall immune response.

In contrast, HLA-DD does not exist as a recognized class II molecule within the MHC. This distinction reinforces why the selection of HLA-DD as the answer highlights the understanding of the types and functions of MHC molecules in immunology.