Practice question

CD3 defines T lineage cells as part of TCR complex. CD4 and CD8 are mutually exclusive co receptors on mature T cells, but some innate lymphocytes share markers. Natural Killer cells are CD3 negative normally, yet subset descriptions and some gating strategies include activated NKT like phenotypes. However monocytes are CD3 negative CD4 positive, B cells CD19 positive CD3 negative. A CD3 positive CD4 negative pattern suggests cytotoxic T or NK like cells lacking CD4. True CD3 positive without CD4 points toward CD8 T or NKT and among given choices NK related pattern is assigned.