agglutinations

Agglutination is the clumping of particles, typically caused when antibodies cross-link antigens on the surfaces of cells or other particles. In immunology and microbiology, agglutination reactions are used to detect the presence of specific antibodies or antigens. The process arises when multivalent antibodies bind to multiple epitopes, linking particles into a lattice that becomes visible as clumps. Factors such as antibody valency, antigen density, temperature, and ionic strength influence the reaction; overstimulation or low reactant concentrations can lead to prozone or postzone effects, and nonspecific factors can produce false positives.

Common formats include direct agglutination, where target cells (like red blood cells) bearing antigen are mixed with antibody; and indirect or passive agglutination, in which inert particles (often latex beads) are coated with antigen or antibody to facilitate detection. Hemagglutination uses red blood cells as carrier particles; reverse or indirect agglutination uses soluble antigens captured by coated beads. Agglutination assays underpin blood typing (ABO and Rh), microbial identification, and some clinical diagnostics.

In linguistics, agglutination is a morphological process in which words are formed by stringing together discrete morphemes, each with a specific meaning and clear boundaries, as in Turkish or Finnish; this contrasts with fusional and isolating languages.

History: The discovery of agglutination reactions in blood typing by Karl Landsteiner and colleagues in the early 20th century revolutionized transfusion medicine.