Antibody production involves preparation of antigen samples and their safe injection into laboratory or farm animals so as to evoke high expression levels of antigen-specific antibodies in the serum, which can then be recovered from the animal. Polyclonal antibodies are recovered directly from serum (bleeds). Monoclonal antibodies are produced by fusing antibody-secreting spleen cells from immunized mice with immortal myeloma cell to create monoclonal hybridoma cell lines that express the specific antibody in cell culture supernatant.
Immunization Schedule for Mice:
- Day 0: Collect pre-immune serum from the mouse to use as a blank when performing ELISA screening after immunization. Store frozen. Inject 50 to 100µg of immunogen (equal to 100 to 200µL of antigen-adjuvant mixture) per mouse. Typical routes of injection include intraperitoneal (i.p.) or subcutaneous (s.c.). One or two such injections may be made per animal.
- Day 14: Boost with an equivalent amount of immunogen in adjuvant.
- Day 21: Test bleed and assay antibody response by ELISA. (Typically, mice are bled under anesthesia through the tail vein or the retro-orbital plexis).
- Day 28: Boost again if necessary. Continue with a similar schedule of alternating boosts and test bleeds until a satisfactory response is observed. For monoclonal antibody production, inject either i.p. or intravenously (i.v.) 4 to 5 days before fusion with the immunogen dissolved in saline (no adjuvant).
Antibody purification involves selective enrichment or specific isolation of antibodies from serum (polyclonal antibodies), ascites fluid or cell culture supernatant of a hybridoma cell line (monoclonal antibodies). Purification methods range from very crude to highly specific and can be classified as follows:
- Physicochemical fractionation – differential precipitation, size-exclusion or solid-phase binding of immunoglobulins based on size, charge or other shared chemical characteristics of antibodies in typical samples. This isolates a subset of sample proteins that includes the immunoglobulins.
- Class-specific affinity – solid-phase binding of particular antibody classes (e.g., IgG) by immobilized biological ligands (proteins, lectins, etc.) that have specific affinity to immunoglobulins. This purifies all antibodies of the target class without regard to antigen specificity.
- Antigen-specific affinity – affinity purification of only those antibodies in a sample that bind to a particular antigen molecule through their specific antigen-binding domains. This purifies all antibodies that bind the antigen without regard to antibody class or isotype.
Antibodies that were developed as monoclonal antibody hybridoma cell lines and produced as ascites fluid or cell culture supernatant can be fully purified without using an antigen-specific affinity method (third type) because the target antibody is (for most practical purposes) the only immunoglobulin in the production sample. By contrast, for polyclonal antibodies (serum samples), antigen-specific affinity purification is required to prevent co-purification of nonspecific immunoglobulins. For example, generally only 2-5% of total IgG in mouse serum is specific for the antigen used to immunize the animal. The type(s) and degree of purification that are necessary to obtain usable antibody depend upon the intended application(s) for the antibody.