Practice question

Mature alpha beta T cells are divided by co receptor expression. CD3 confirms T cell lineage as invariant chain of TCR. CD4 binds MHC class II and marks helper T cells that secrete cytokines to activate B cells and macrophages. CD3 positive CD4 positive cells are therefore classic helper T lymphocytes, distinct from cytotoxic CD3 CD8 cells, CD3 negative NK cells that express CD56, CD3 negative monocytes expressing CD14, and CD19 positive B cells. This double positive phenotype is fundamental in HIV monitoring and immunophenotyping.