Developing tools for learning immunology using diffusion-based salt precipitation assays: A low-cost alternative for college laboratories.

The Ouchterlony double immunodiffusion technique is used as a teaching tool for studying immune responses and exemplifying differences in antigen-antibody reactions. Although commonplace in undergraduate labs, standardized commercial kits limit learning experiences because they have fixed modalities of use, a low shelf-life, and impose budgetary constraints in the long-term, collectively posing an economic challenge. To mitigate these problems, this study attempts to simulate various types of 'antigen-antibody' reactions using combinations of Mg, Mn, Cu and Ag salts that form a precipitate with BaSO₄. Using an optimized format of thin agar plates, different salts precipitation reactions were monitored over a time course of "immunodiffusion". These reactions were demonstrably versatile towards simulating (i) quantitation of differential titer among antibodies, (ii) determining serological-identity versus non-identity, (iii) quantitative demonstration of the prozone phenomenon, and finally; (iv) using double precipitin reactions to simulate combinations of antibodies in the same sample. As part of a laboratory exercise, these parameters were used to design an open-ended query aimed to check the effectiveness of student engagement and learning outcomes. Undergraduate students were able to conduct the experiment in a shorter time frame, and interpreted their observations in a multidimensional manner. This allowed teachers to add to the discussion leading to an efficient model of collaborative learning. The salt-precipitation format of "immunodiffusion" is thus not only economical and quick, but allows for flexibility to simulate problems that are of immediate relevance.