What happens to an antigen once it encounters a lymphocyte?

When an antigen encounters a lymphocyte, it essentially engages with the immune cell, triggering a specific response. The correct answer indicates that the antigen will no longer circulate freely in the bloodstream or the extracellular environment. This occurs because, upon binding to a lymphocyte, the antigen is typically processed or internalized by the lymphocyte, particularly in the case of B cells or T cells.

B cells may internalize the antigen, process it, and present it on their surface in combination with major histocompatibility complex (MHC) molecules to T cells. This antigen-lymphocyte interaction is crucial for initiating an adaptive immune response. The antigen is not just annihilated on contact but is rather recognized, and this interaction facilitates the activation and proliferation of lymphocytes, which will generate a more robust defense against that specific antigen.

In conclusion, the process ensures that the antigen is effectively engaged and utilized in the immune response rather than allowing it to continue circulating, which would prevent an effective immune reaction from occurring.