Jc. Thompson et al., KINETICS AND PROPOSED MECHANISM OF THE REACTION OF AN IMMUNOINHIBITION, PARTICLE-ENHANCED IMMUNOASSAY, Clinical chemistry, 43(12), 1997, pp. 2384-2389
We report kinetic studies on the reaction of a latex agglutination imm
unoassay used to quantify phenytoin in serum. In this assay, polystyre
ne particles with a covalently attached analog of phenytoin react with
an antiphenytoin monoclonal antibody to form light-scattering aggrega
tes, with the rate of this reaction being decreased by addition of phe
nytoin from sample. In the absence of free (sample) phenytoin, this re
action did not exhibit a maximum rate of agglutination in the presence
df excess antibody, i.e., an equivalence point. Furthermore, agglutin
ation was inhibitable by free phenytoin even when the latter was added
after agglutination of particles with antibody had begun. Most signif
icantly, the immunoagglutination proceeded in an identical fashion wit
h monovalent F(ab) fragment. These data are consistent with low-affini
ty immunospecific particle-antibody complexation, which then induces c
olloidal aggregation, without requiring immunospecific bridging by ant
ibody molecules. The described mechanism is not generalizable to all l
atex agglutination immunoassays, although disturbance of colloidal sta
bility may be a component in most assays.