Antigen-specific antibody, measurement

Evaluating the immune response to the vaccine at the same time as evaluating toxicity is recommended in a 2003 WHO guideline (Table 31.1). This makes good sense because any toxicity observed with vaccines is frequently related to the immune response, and correlation of these two endpoints provides a fuller explanation of the test results. Assays to measure the immune response include those which measure antigen-specific antibody responses (e.g., ELISA) and cell-mediated responses (e.g., y-interferon—ELISPOT). Developing these... 

TABLE 84—7. Potential Indications for Measurement of Antigen-specific Antibody... 

There are many indications for the measurement of antigen-specific antibody. Some common indications are listed in Table 84-7. Methods to perform these measurements include enzyme-linked... 

An alternative to the traditional in vivo TDAR assay is the recently developed in vitro human lymphocyte activation (HuLA) assay using human peripheral blood mononuclear cells (PBMCs), which measures secondary influenza-specific responses. This assay is sensitive to, and can differentiate the responses of, a number of known immunosuppressive compounds with different mechanisms of action at concentrations within their respective therapeutic ranges. Various endpoints can be evaluated, including proliferation and flu antigen-specific antibody (IgM and lgG)-secreting cells (Collinge et al., 2010). 

Radioimmunoassay (RIA). RIA is a procedure used to detect or determine an antigen in a sample based on immunology. A radioisotope-labelled antigen is mixed into a sample, an antigen specific antibody is added to the mixture, and the amount of antibody bound with radiolabeled antigen is then measured by scintillation counter. The amount of antigen in the sample is calculated from the radioactivity. RIA is more sensitive than ELISA, but ELISA has replaced RIA because the latter requires the use of radioactive compounds. 

Standardization and Testing. RequHements for DTP have been described (17). Standardization of potency for the toxoids reHes on antigenic and flocculation tests. In principle, the antigenic tests are conducted to measure the abUity of the vacciae to Hiduce specific antibodies Hi guHiea pigs. The flocculation test provides a quantitative estimate of the amount of toxoid Hi the vacciae. 

Immunoassay is the sterile measurement of a drug molecule as an antigen using a specific antibody. Detection is performed by UV light absorption, radioactivity, or fluorescence polarization. 

Enzyme-linked immunosorbent assay (ELISA) is based on the specific reaction between an antibody and an antigen. One of the reagents in the reaction is labeled with an enzyme that generates a colorimetric product that can be measured with a spectrophotometric device. The color intensity correlates with the concentration of specific antibody and the respective antigen. The reaction can be formatted in various ways in a multiwell plate (microtiter plate) with the common formats being the sandwich assay, the competitive assay, and the direct assay. (See Figure 11.1.)... 

The blood samples are sent to a contract laboratory for measurement of antigen-specific (in this case, tetanus toxoid) antibodies. 

Some colored compounds have also been linked to peptides or proteins for the detection and measurement within visible spectra ranges. Colorimetric methods are relatively nonspecific but they can be made specific by linking them to enzymatic or immunologic reactions (see Immunoassay section). In these cases, enzymes produce colored products from colorless substrates, rather than radionuclides, are used to label particular antigens and antibodies (Winder and Gent 1971). 

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