What does crossed lines between wells in an Ouchterlony plate indicate?

In the context of an Ouchterlony double diffusion test, crossed lines between wells indicate nonidentity between the antigens being tested. This result occurs when the two antigens do not share any common epitopes, which means that they do not have any structural or functional similarities that could cause them to precipitate together.

In this test, the pattern of diffusion and precipitation is critical for interpreting the relationships between antigens. When two antigens are run in separate wells on a gel and they are completely different, they will diffuse independently and create distinct lines that intersect each other at an angle. This crossing signifies that there is no recognition or binding between the antibodies produced against each antigen.

Understanding this characteristic of crossed lines is important in immunology, as it helps in differentiating between the nature of antigen interactions, which can be crucial for diagnostic purposes in serology and blood banking.