Figure 2.

The production of IgG antibodies depends on a specific interaction between CD4 + T cells and B cells. 1: The B cell receptor recognizes an epitope on a foreign HLA molecule. 2: This leads to internalization of the target antigen, which is then degraded into peptides. 3: Some of these peptides bind to the HLA class II molecules on the B cell and the foreign (nonself) peptides are recognized by CD4 + T cells. 4: his leads to activation of the T cells associated with the production of immunoregulatory molecules. 5: These molecules trigger a class switch of the antibodies produced.