A COMMON EPITOPE ON PLATELET INTEGRIN ALPHA(IIB)BETA(3) (GLYCOPROTEINIIBIIIA-CD41B CD61) AND ALPHA(M)BETA(2) (MAC-1-CDIIB/CD18) DETECTED BY A MONOCLONAL-ANTIBODY/

Evidence is presented that the mAb 25E11, directed against the platele t integrin alpha(IIb)beta(3) (glycoprotein IIbIIIa; CD41b/CD61) also b inds the distinct myeloid cell integrin alpha(M) beta(2) (Mac-1; CDIIb /CD18). The Ab is shown to identify only the alpha IIb beta 3 integrin complex and not the individual subunits in crossed Ab immunoelectroph oresis of platelet lysate. From cultured human macrophages, sequential immunoprecipitation of labeled glycoproteins indicated that 25E11 als o bound the Mac-1 (CD11b/CD18) complex. This was confirmed using COS-7 and WOP cells doubly transfected with alpha(M) (CD11b) and beta(2) (C D18) or with alpha(L) (CD11a) and beta(2) when it was found that the A b bound only the alpha(M) beta(2) transfectants. Studies with these ce lls and the RC2A myeloid cell line stimulated with tetradecanoyl phorb ol acetate or FMLP indicated that the 25E11 epitope on Mac-1 did not d epend on cell activation for its expression. The rationale for this cr oss-reactivity is not known, but since the 25E11 Ab inhibits the funct ion of both platelets and myeloid cells, it is likely that this shared epitope is important to integrin function. Given the expression of th is epitope on IIbIIIa and Mac-1, the dominant integrins of platelets a nd granulocyte/macrophage cells, but not on other integrins, a role of this epitope in the early events of inflammation is suggested.