Immunophenotypic markers

Question 1

CD1a

Answer 1

Transmembrane glycoprotein related to MHC.

Expressed on APCs, especially Langerhans cells. Also positive in cortical thymocytes and some T-ALLs.

Question 2

CD2

Answer 2

Leukocyte function antigen 2 (LFA2), binds CD58 (LFA3) on APCs to improve T-cell stimulation.

Expressed in T-lymphocytes, from the subcapsular thymocyte stage onwards.

Question 3

CD3

Answer 3

Co-receptor for TCR. Widely used as a pan-T-cell marker. Also known as “OKT3”.

Expressed in T-lymphocytes, initially cytoplasmic but surface-expressed from thymocyte stage onwards.

Question 4

CD4

Answer 4

Co-receptor of TCR, specifies MHC class II restriction. Also the main receptor for HIV binding.

Expressed in helper T-cells and T-regs.

Question 5

CD5

Answer 5

Antigen of unknown function. Expressed in T-lymphocytes from subcapsular thymocyte stage onwards.

Used to identify T-cells and T-cell lymphomas, also CLL and thymic carcinoma.