A method of detecting and isolating cells that produce high levels of a heterodimeric protein having a first subunit and a second subunit, the method comprising: (a) transfecting cells with a nucleic acid that encodes a cell surface capture protein (CSCP), which is a fusion protein comprising an antigen-binding protein and a membrane anchor domain, wherein the cell expresses the heterodimeric protein, wherein the heterodimeric protein comprises multiple subunits and a first site on the heterodimeric protein resides on a first subunit comprising a heavy chain comprising a wild type CH3 domain having a histidine residue at position 95 according to the IMGT exon numbering system and a tyrosine residue at position 96 according to the IMGT exon numbering system, and a second site on the heterodimeric protein resides on a second subunit comprising a heavy chain comprising a substituted CH3 domain having an arginine residue at position 95 according to the IMGT exon numbering system and a phenylalanine residue at position 96 according to the IMGT exon numbering system, wherein the CSCP comprises an ScFv capable of binding the first subunit but not the second subunit of the heterodimeric protein, and wherein (i) the CSCP binds to the first site on the heterodimeric protein to form a CSCP- heterodimeric protein complex inside the host cell, (ii) the CSCP- heterodimeric protein complex is transported through the host cell, and (iii) then displayed on the surface of the host cell; (b) detecting a cell of (a) that expresses the CSCP in high yield; (c) isolating and culturing the cell that expresses the CSCP in high yield; (d) detecting the heterodimeric protein on the surface of the isolated and cultured cell of step (c) with a detection molecule that binds the second site on the heterodimeric protein, wherein the detection molecule comprises a recombinant antigen-binding protein that specifically binds the substituted CH3 domain having an arginine residue at position 95 according to the IMGT exon numbering system and a phenylalanine residue at position 96 according to the IMGT exon numbering system; and (e) isolating the cell detected in step (d) that bears the detected heterodimeric protein on its surface. (a) transfecting cells with a nucleic acid that encodes a cell surface capture protein (CSCP), which is a fusion protein comprising an antigen-binding protein and a membrane anchor domain, wherein the cell expresses the heterodimeric protein, wherein the heterodimeric protein comprises multiple subunits and a first site on the heterodimeric protein resides on a first subunit comprising a heavy chain comprising a wild type CH3 domain having a histidine residue at position 95 according to the IMGT exon numbering system and a tyrosine residue at position 96 according to the IMGT exon numbering system, and a second site on the heterodimeric protein resides on a second subunit comprising a heavy chain comprising a substituted CH3 domain having an arginine residue at position 95 according to the IMGT exon numbering system and a phenylalanine residue at position 96 according to the IMGT exon numbering system, wherein the CSCP comprises an ScFv capable of binding the first subunit but not the second subunit of the heterodimeric protein, and wherein (i) the CSCP binds to the first site on the heterodimeric protein to form a CSCP- heterodimeric protein complex inside the host cell, (ii) the CSCP- heterodimeric protein complex is transported through the host cell, and (iii) then displayed on the surface of the host cell; (b) detecting a cell of (a) that expresses the CSCP in high yield; (c) isolating and culturing the cell that expresses the CSCP in high yield; (d) detecting the heterodimeric protein on the surface of the isolated and cultured cell of step (c) with a detection molecule that binds the second site on the heterodimeric protein, wherein the detection molecule comprises a recombinant antigen-binding protein that specifically binds the substituted CH3 domain having an arginine residue at position 95 according to the IMGT exon numbering system and a phenylalanine residue at position 96 according to the IMGT exon numbering system; and (e) isolating the cell detected in step (d) that bears the detected heterodimeric protein on its surface.