A human leukocyte differentiation antigen family with distinct alpha-subunits and a common beta-subunit: the lymphocyte function-associated antigen (LFA-1), the C3bi complement receptor (OKM1/Mac-1), and the p150,95 molecule.

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Abstract
The human lymphocyte function-associated antigen-1 (LFA-1), the complement receptor-associated OKM1 molecule and a previously undescribed molecule termed pl50,95, have been found to be structurally and antigenically related. Each antigen contains an .alpha.- and .beta.-subunit noncovalently associated in an .alpha.1.beta.1-structure as shown by cross-linking experiments. LFA-1, OKM1 and p150,95 .alpha.-subunit designations and their MW [in daltons] are .alpha.L = 177,000, .alpha.M =165,000 and .alpha.X = 150,000, respectively. The .beta.-subunits are all = 95,000. Some MAb [monoclonal antibodies] precipitated only LFA-1, others only OKM1, and another precipitates all 3 antigens. The specificity of these MAb for particular subunits was examined after subunit dissociation by high pH. MAb specific for LFA-1 or OKM1 bind to the .alpha.L- or .alpha.M-subunits, respectively, while the crossreactive MAb binds to the .beta.-subunits. Coprecipitation experiments with intact .alpha.1.beta.1-complexes showed anti-.alpha. and anti-.beta. MAb can precipitate the same molecules. In 2-dimensional (2D) isoelectric focusing-SDS-PAGE [sodium dodecyl sulfate-polyacrylamide gel electrophoresis], the .alpha. subunits of the 3 antigens are distinct, while the .beta.-subunits are identical. Biosynthesis experiments showed .alpha.L, .alpha.M and .alpha.X are synthesized from distinct precursors, as is .beta.. The 3 antigens differ in expression on lymphocytes, granulocytes and monocytes. During maturation of the [human lymphoma] monoblast-like U937 line, .alpha.M and .alpha.X are upregulated and .alpha.L is downregulated. Some MAb to the .alpha. subunit of OKM1 inhibited the complement receptor type 3. LFA-1, OKM1 and pl50,95 constitute a novel family of functionally important human leukocyte antigens that share a common .beta.-subunit.