Detecting cells secreting a protein of interest

1. A method for labeling a cell producing an antigen-specific antibody, the method comprising:

obtaining a cell sample containing multiple antibody-producing cells;

tagging the antibody-producing cells with a cross-linking reagent, wherein the cross-linking reagent has a first portion configured to bind to a cell surface marker that is specific to the antibody-producing cells and a second portion configured to bind to an antigen of interest;

exposing the antibody-producing cells to the antigen of interest such that the antibody-producing cells become linked through the cross-linking reagent to the antigen of interest;

allowing the antibody-producing cells to produce antibodies, such that a portion of the antibody-producing cells produce the antigen-specific antibody, which binds to the antigen of interest; and

exposing the antibody-producing cells to a labeled secondary antibody configured to bind to the antigen-specific antibody.

2. The method of claim 1 , wherein the first portion of the cross-linking reagent comprises a F AB fragment configured to bind to the cell surface marker that is specific to the antibody-producing cells.

3. The method of claim 1 , wherein the second portion of the cross-linking reagent comprises a F AB fragment configured to bind to the antigen of interest.

4. The method of claim 1 , wherein the second portion of the cross-linking reagent comprises the antigen of interest.

5. The method of claim 4 , wherein the antibody-producing cells are exposed to the antigen of interest when then the antibody-producing cells are tagged with the cross-linking reagent.

6. The method of claim 1 , wherein the exposing the antibody-producing cells to the antigen of interest comprises exposing the antibody-producing cells to a substrate having the antigen of interest bound thereto.

7. The method of claim 6 , wherein the substrate is selected from the group consisting of a bead, a cell, and combinations thereof.

8. The method of claim 1 , wherein the exposing the antibody-producing cells to the antigen of interest comprises exposing the antibody-producing cells to a free-floating form of the antigen of interest.

9. The method of claim 1 , further comprising identifying cells that are labeled by the secondary antibody.

10. The method of claim 1 , wherein the first portion of the cross-linking reagent comprises a ligand configured to bind to the cell surface marker that is specific to the antibody-producing cells, wherein the ligand does not comprise a F AB fragment.

11. The method of claim 1 , wherein the antigen of interest is an antibody.

12. A method for labeling cells that produce a protein of interest, the method comprising:

obtaining a cell sample containing protein-producing cells;

tagging the protein-producing cells with a cross-linking reagent, wherein the cross-linking reagent comprises a first portion adapted to bind to a cell surface marker that is specific to the protein-producing cells and a second portion that is configured to be bound to a first ligand, wherein the first ligand specifically binds to the protein of interest;

exposing the protein-producing cells to the first ligand, such that the protein-producing cells become linked through the cross-linking reagent to the first ligand;

allowing the protein-producing cells to produce the protein of interest; and

exposing the protein-producing cells to a labeled antibody that is adapted to bind to the protein of interest.

13. The method of claim 12 , wherein the first portion of the cross-linking reagent comprises a F AB fragment configured to bind to the marker that is specific to the protein-producing cells.

14. The method of claim 12 , wherein exposing the protein-producing cells to the first ligand comprises: exposing the protein-producing cells to a free-floating form of the first ligand.

15. The method of claim 12 , wherein exposing the protein-producing cells to the first ligand comprises: exposing the protein-producing cells to a substrate having the first ligand bound thereto.

16. The method of claim 15 , wherein the object is a substrate that is connected to the first portion of the cross-linking reagent via a biotin/streptavidin link.

17. The method of claim 15 , wherein the substrate is selected from the group consisting of a bead, a cell, and combinations thereof.

18. The method of claim 12 , wherein the labeled secondary antibody is an anti-IgG antibody.

19. The method of claim 12 , further comprising identifying the cells that are labeled by the labeled antibody.

20. The method of claim 12 , wherein the first portion of the cross-linking reagent comprises a second ligand configured to bind to the cell surface marker that is specific to the protein-producing cells, wherein the second ligand does not comprise a F AB fragment.

21. The method of claim 12 , wherein the first ligand is a protein-specific antibody that specifically binds to the protein of interest.

22. The method of claim 21 , wherein exposing the protein-producing cells to the protein-specific antibody comprises exposing the protein-producing cells to a free-floating form of the protein-specific antibody.

23. The method of claim 21 , wherein the step of exposing the protein-producing cells to the protein-specific antibody comprises: exposing the protein-producing cells to a substrate having bound.

24. The method of claim 23 , wherein the substrate is connected to the first portion of the cross-linking reagent via a biotin/streptavidin link.

25. The method of claim 19 , wherein the substrate is selected from the group consisting of a bead, a cell, and combinations thereof.