Final answer:
T cells recognize antigens that are processed and presented by MHC molecules. Unlike T cells, B cells can bind to native unprocessed antigens. The incorrect statement is that native antigens recognized by T cells activate B cells; thus, the correct answer is option 4.) It activates B cells.
Step-by-step explanation:
The question concerns the characteristics of native antigens recognized by T cells. T cells recognize antigens in a very specific manner. Antigens must be processed and presented by MHC molecules to be recognized by T cell receptors. This processing and presentation is done by antigen-presenting cells. T cells are designed to not recognize self-proteins during their maturation in the thymus; they undergo a selection process that ensures their receptors are tolerant to self-antigens. To activate T cells, antigens must be foreign and presented by MHC molecules.
However, when it comes to B cells, the scenario is quite different. B cells can recognize unprocessed, native antigens without the need for MHC molecules. They are capable of binding to antigens directly through their surface-bound antibodies, known as B cell receptors (BCRs). B cells can act as antigen-presenting cells and present antigens to helper T cells via class II MHC, but their primary function does not typically involve activating B cells by themselves.
In the context of T cell-dependent activation of B cells, both the B and T cells must communicate closely. B cells internalize the recognized antigen, process it, and present it on class II MHC molecules to helper T cells. The interaction with helper T cells then provides a second signal through cytokines, which fully activates the B cells, leading them also to act as antigen-presenting cells.
In contrast, T cell-independent activation of B cells involves antigen recognition without the processing and presentation to T cells. This direct activation, usually by repeated nonprotein antigens like polysaccharides, leads mainly to the production of IgM antibodies.
Given this information, amongst the provided choices, the characteristic that is not true for native antigens recognized by T cells is that 'It activates B cells'. Therefore, the correct option is 4) It activates B cells.