An elevated proportion of T cells that express human leukocyte antigen (HLA)-DR. HLA-DR is an MHC class II cell surface receptor that presents antigens (peptides of at least 9 amino acids), thereby constituting a ligand for the T-cell receptor. HLA-DR can be upregulated in response to immune stimulation. [ http://www.ncbi.nlm.nih.gov/pubmed/11531958 ]