CD68 and severe acute respiratory syndrome: The frequency of distinct lung leukocyte populations, including macrophages (CD68 + HLADR+), dendritic cells (DCs; CD68-HLADR + CD11c+), CD8 T lymphocytes (CD3 + CD8+), and B cells (CD3-CD20+) differed in the two age groups during SARS-CoV infection (Figure 5B-E).