IMMUNOLOGY

Detailed explanation-1: -The HLA class II molecules expressed by antigen-presenting cells present peptide antigens to CD4 T cells (Fig. 9.1). DQ and DR are two of five isotypes of HLA class II proteins; heterodimers composed of and chains, encoded by the highly polymorphic loci HLA-DQ and-DR, respectively.

Detailed explanation-2: -HLA class II genes are the most important genes associated with the risk of inheriting Type I diabetes, accounting for about 40-50% of heritability. Alleles of these genes that affect peptide binding to the MHC class II molecules seem to impact Type I diabetes risk the most.

Detailed explanation-3: -HLA class I molecules are expressed on the surface of almost all nucleated cells. Class II molecules are expressed only on B lymphocytes, antigen-presenting cells (monocytes, macrophages, and dendritic cells), and activated T lymphocytes.

Detailed explanation-4: -The HLA DQ Association test detects celiac disease-associated alleles that predispose to the disorder but is not diagnostic of celiac disease. More than 95% of celiac disease patients are positive for DQ2, half DQ2, or DQ8, but many individuals with these genetic results do not develop celiac disease.