Final answer:
Naïve B cells internalize specific antigens through endocytosis within the germinal centers of lymph nodes and present peptide fragments on their surface paired with MHC class II proteins, facilitating recognition by T cells.
Step-by-step explanation:
When naïve B cells encounter their specific antigen (usually in the germinal centers of the lymph node), the antigen is brought into the B cell by endocytosis. The peptide fragments of the antigen are displayed on the surface of the cell bound to major histocompatibility complex (MHC) class II proteins.
The immune process can be detailed as follows: B cells, after maturing in the bone marrow, migrate to lymph nodes or other lymphatic organs. When they encounter an antigen that binds to their specific receptor, they internalize the antigen through endocytosis. The antigen is then processed and fragmentized into peptides, which are later presented on the cell surface in conjunction with MHC class II molecules. This antigen presentation is crucial for the recognition by T cells, which further leads to B cell activation and antibody production.