What is the role of the plasma cell in the antigen-antibody response? makes an antigen harmless without destroying it produces antibodies against the sensitizing antigen produces antibodies after an exposure to a known antigen clumps antibody-antigens linkages together to form immune complexes?

The correct answer is that it produces antibodies against the sensitizing antigen.  

Plasma cells are formed in the bone marrow, the B cells divide into plasma cells, which generate molecules of antibody. Once discharged into the lymph and blood, these antibody molecules combine with the target antigen, that is, foreign substance and starts its destruction or neutralization.  

this protocol provides a detailed procedure for agarose-based ip to purify and enrich the protein of interest.