The production of both antibodies starts off the same. Scientists inject the antigen along with an adjuvant (to stimulate immune response) into an naïve animal. The animal generates an immune response, and B-cells start to proliferate and generate a repertoire of antibodies that can target the antigen.
Each B-cell generates a different antibody that looks for different thing (epitope) on the antigen.
To make the polyclonal antibodies, you simply extract the serum from the blood of the animal. The serum, also known as antiserum, contains the polyclonal antibodies which can target multiple targets. The varying target ability of polyclonal antibodies is due to its collection of antibodies coming from multiple B-cells. However, this raises concern regarding the batch-to-batch variation because of affinity maturation and class switch recombination.
To make monoclonal antibodies, after injection, you collect the B-cells that present different antibodies on the surface. Then, fuse B-cell with immortalized B-cell because B-cell normally has a relatively short lifetime. After fusion, you create a hybridoma. Then you need to select which hybridoma is the best to detect your antigen, by testing with western blotting or dilution approach. After that, you select the best hybridoma and that’s the immortalized cell line that can give you a continuous amount of monoclonal antibodies.