Human CD4 is a cell surface glycoprotein of 55 kd expressed on most thymocytes, on about two thirds of peripheral T cells, and on some monocyte macrophage lineage cells. CD4 interacts with MHC Class II molecules in an accessory role during foreign antigen recognition by T cells （3）. The extracellular portion of CD4 is an array of four Ig-like domains. The amino terminal region of CD4 is a receptor for the HIV-1 viral protein gp120.

Antibodies QS4120 and M-T441 （cat #148-020） each bind to a distinct epitope of CD4 and are suitable as a matched pair for EIA using QS4120 as capture and Biotinylated M-T441（cat# 148-030） as detector.

Isotype: Murine IgG1

Immunogen: CD4+ transfectant/human CEM

Specificity: Antibody QS4120 recognizes the domain 1 region of the CD4 molecule （1, 2）.

Functional Application: Antibody QS4120 will block binding of HIV-1 gp120 protein to CD4 （4） and also blocks HLA Class II Rosette formation.