Of the 56 cysteines in the extracellular domain of the CD18 antigen (β2 integrin subunit), corresponding ones are not found in 12 positions in the β4, β7, or β8 integrin subunits. These 12 cysteines were mutated to alanines, either singly or in pairs, in CD18. All these mutants can support the expression of all three CD11/CD18 integrins. Transfectants expressing these variant integrins are generally more adhesive than the wild-type, suggesting that the cysteine residues, perhaps by engaging in disulphide bonds, may contribute to the maintenance of the CD11/CD18 integrins in a resting state.
