The rat anti-mouse CD49b monoclonal antibody (clone DX5) specifically binds to the integrin α2 chain (CD49b). CD49b is a 150 kDa transmembrane glycoprotein that non-covalently associates with CD29 (integrin β1) to form the integrin α2β1 complex known as VLA-2. The rat anti-mouse CD49b antibody (clone DX5) has been reported to identify the majority of NK cells and a small T-cell subpopulation in most mouse strains (e.g., A/J, AKR, BALB/c, C3H/HeJ, C57BL/6, C57BL/10, C57BR, C58, CBA/Ca, DBA/1, DBA/2, SJL, SWR, 129/J, but not NOD). The DX5 antibody also recognizes platelets that express high levels of CD49b. Multiparameter flow cytometric analysis has demonstrated that most lymphocytes which express NK-1.1 (NKR-P1B and NKR-P1C), as detectable by mouse anti-mouse NK-1.1 antibody (clone PK136), also express the DX5 antigen. Small DX5+ NK-1.1- and DX5- NK-1.1+ cell subsets are found, especially among the CD3-positive cell population. Some CD49b+ NK cells have been reported to gradually lose reactivity with the rat anti-mouse CD49b antibody (clone DX5) when cultured in the presence of recombinant human IL-2. The resulting DX5-negative cells have weakened cytotoxic activity when compared to the remaining DX5+ cells. This indicates that the DX5 antibody distinguishes functional subsets of NK cells. No activation or blocking activity of the rat anti-mouse antibody (clone DX5) has been observed. Staining of splenic NK cells with this antibody reportedly can be blocked by hamster anti-mouse CD49b antibody (clone HMα2).