Haptens are small molecules that are unable to elicit an immune response on their own but can do so when they bind to larger carrier molecules, resulting in the formation of a complex called a hapten-carrier complex. These carrier molecules can be proteins, such as albumin or hemoglobin, or synthetic polymers.
When a hapten-carrier complex is formed, the immune system recognizes the complex as foreign and mounts an immune response against it. This immune response can result in the production of antibodies specific to the hapten-carrier complex. This process, known as haptenization, can be used to create antibodies for various applications, including diagnostics, therapeutics, and research.