Final answer:
A hapten becomes immunogenic by binding to a larger carrier molecule to form a complex that can then stimulate an immune response. This complex is processed by antigen-presenting cells, leading to antibody production against the hapten by B cells.
Step-by-step explanation:
A hapten can become immunogenic through conjugation with a carrier protein. A hapten alone is too small to elicit an immune response. Its molecular structure lacks the complexity needed to provoke the necessary interactions with immune cells. However, when a hapten binds to a larger protein molecule, it forms a hapten-carrier complex that can be recognized as antigenic. This complex can then be processed by antigen-presenting cells, which display the hapten as part of an antigen-MHC (Major Histocompatibility Complex) complex on their surface to T cells. The T cells can help activate B cells, which then produce antibodies against the hapten.
Instances of haptens becoming immunogenic include the molecule urushiol from poison ivy and penicillin, which can cause allergic reactions in some individuals. It's important to note that the recognition of the antigen-hapten complex by B cells and their subsequent activation often involves helper T cells, especially with protein antigens which are T-dependent. However, irrespective of whether the antigen is T-dependent or independent, the initial step for a hapten to become immunogenic is its conjugation with a carrier protein.