This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Antigen-antibody reaction, Subject name: Microbiology
Maximum Lattice formation occurs in - 
Select and explain. 
A. Zone of antibody excess, B. Zone of antigen excess, C. Zone of equivalence, D. Can occur in any zone
C: Zone of equivalence
Answer: C: Zone of equivalence 
Explanation: Ans. is 'c' i.e., Zone of equivalence o The lattice hypothesis was proposed by marrack (1934) to explain the mechanism of precipitationo According to this concept, multivalent antigens combine with bivalent antibodies in varying proportion depending on the antigen-antibody ratio in the reacting mixture.o Precipitation results when large lattice is formed consisting of alternating antigen and antibody molecules. This is possible only in the zone of equivalence.o In the zone of antigen or antibody excess, the lattice does not enlarge, as the valencies of the antibody and the antigen, repectively are fully satisfied. In either cases extensive lattice cannot be formed and precipition is inhibitedo The lattice hypothesis holds good for agglutination also.