Antigen development

Characteristics of the target analyte such as molecular weight, three-dimensional structural complexity, and solubility properties all play an important role in the development or selection of useful antigens. Identifying exactly what the assay should and should not detect is another critical piece of information that needs to be taken into account in antigen development or selection. 

Although molecules with molecular mass greater than 5000 da, such as proteins, glycoproteins, and carbohydrates, can readily elicit a potent antibody formation, molecules such as drugs that have low molecular masses cannot stimulate an immunogenic response. These molecules, widely known as haptens, will bind with preformed antibodies but will not cause antibodies to be produced. 

To become immunogenic, a hapten has to be linked with a large molecule, such as a protein, prior to its introduction into the host animal. Several proteins can act as such carrier molecules including bovine serum albumin, human serum albumin, ovalbumin, thyroglobulin, poly-L-lysine, and hemocyanin. Among these proteins, bovine serum albumin is most commonly used because it is inexpensive, readily available, very soluble, highly immunogenic, and, in addition, resists denaturatlon (3). 

Functional groups on haptens that are mostly used for linkage are the amino and carboxyl groups. As a result, the most common linkages are peptide bonds between a carboxyl and an amino group. Other groups that can be also used for 

The chemistry and orientation used in attaching the hapten to the carrier molecule have a great impact on the specificity of the antibodies subsequently elicited. Specificity is lost to the region of the hapten molecule involved in the protein linkage because this is sterically shielded from interaction with the immune system. Therefore, the structure of an analyte should be carefully considered in order to design an appropriate antigen based upon the reactivity spectrum desired in the final assay. 

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Tolerance following the intake of a large dose of antigen develops through clonal deletion of specific Thl lymphocytes or increase in the number of antigen nonspecific... 

Contamination of blood products with lymphocytes can lead to transfusion-induced reactions ranging from a mild fever to severe reactions such as alloimmunization and graft versus host disease (GvHD), in which the transfused lymphocytes (graft) survive the defensive immune reaction of the patient (host) and start a reaction which destroys the cells of the host. The patient also may develop an immune response to the human leukocyte antigen (HLA) type of the graft s cells and reject all platelet transfusions that do not match their own HLA system. The HLA system, found on blood platelets and lymphocytes, is more compHcated than, but similar to, the ABO blood group system of red cells. 

Immunoassay is a method that identifies and quantifies unknown analytes usiag antibody—antigen reactions. Techniques are based ia immunochemistry, analytical chemistry, and biochemistry, with a history of development paralleling advances ia microbiology and immunology (see also Immunotherapeutic agents). 

Latex agglutination immunoassays are easily formatted into simple kits which can provide yes/no and semiquantitative estimates of antigen (or antibody) in a sample. The first such assay was developed in 1957 for rheumatoid factor (15) and assays are on the market for the deterrnination of many species of bacteria, fungi. Mycoplasma, parasites, ckettsia, and vimses, as well as for the deterrnination of autoimmune disease, hormones (qv), dmgs (see Pharmaceuticals), and blood proteins (16). Latex agglutination is also the basis of many home pregnancy tests. 

EIAs can be used per se or with a spectrophotometer. Traditionally, EIAs have been developed in 96-weU microtiter plates which provide the immobilization support for the assay, the reaction vessel, and, when linked to a spectrophotometer-based reader, a rapid means to detect and quantify the color resulting from interaction of a substrate with the antibody—antigen—enzyme complex. Automated immunoassay analyzers targeted primarily for use in the clinical laboratory have taken automation one step further, utilizing robotics to carry out all reagent additions, washings, and final quantification including report preparation. 

The first SRS-A antagonist, FPL-55712 (26) (149), was discovered before the stmctures of the leukotrienes were detemiined. Although this compound is relatively weak as an antagonist and suffers from a very short half-life in vivo, it played an important role both in leukotriene stmcture elucidation and as a model for later antagonists. In work stmcturaHy related to FPL-55712, LY-171883 was developed (27) (150). LY-171883 was evaluated in several clinical trials before development was stopped. Orally adrninistered, LY-171883 blocked slightly the response to aerosol LTD improved pulmonary function (FEV ) in mild asthmatics (151), decreased the sensitivity of asthmatics to cold air-induced bronchoconstriction (152), and significantly reduced the bronchoconstrictor response to inhaled antigen (153). However, in all these studies the beneficial effects were minimal. 

Rotavirus. Rotavims causes infant diarrhea, a disease which has major socio-economic impact. In developing countries it is the major cause of death in infants worldwide, causing up to 870,000 deaths per year. In the United States, diarrhea is stiU a primary cause of physician visits and hospitalization, although the mortaUty rate is relatively low. Studies have estimated a substantial cost benefit for a vaccination program in the United States (67—69). Two membrane proteins (VP4 and VP7) of the vims have been identified as protective epitopes and most vaccine development programs are based on these two proteins as antigens. Both Hve attenuated vaccines and subunit vaccines are being developed (68). 

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