Pathogens have various types of molecules on their surface and these all act as different antigens. Each one stimulates a different B lymphocyte to clone and produce antibody. The result is a mixtures of antibodies known as polyclonal antibodies, which all attack the pathogen.
If a single B lymphocyte could be made to divide outside the body, then a single monoclonal antibody could be produced. Monoclonal antibodies have important uses. Unfortunately, B cells do not usually divide outside the boddy! However, if the B lymphocyte are fused with cancer cells the resulting cells are called hybridomas. These do divide and they produce antibody.
1) Substance for which monoclonal antibody is required is injected into the animal. Animals B lymphocytes produce antibody against the substance.