Final answer:
Multideterminant antigens are the type of antigens that are complex, highly immunogenic, and recognized by both T cells and B cells. These antigens contain multiple antigenic determinants, allowing for the simultaneous binding of multiple T cell receptors or B cell receptors, critical for a potent and effective immune response.
Step-by-step explanation:
The type of antigens that are recognized by both T cells and B cells, that possess higher complexity, and are generally highly immunogenic are multideterminant antigens. These antigens have multiple antigenic determinants, allowing for multiple bindings with different T cell receptors or B cell receptors. This is evidenced by Figure 21.16, which illustrates the ability of T cells with three different specificities to bind different parts of the same antigen. Similarly, a typical protein antigen can bind different antibodies due to the presence of multiple epitopes, as shown in Figure 18.4. Protein antigens, which are called T-dependent antigens, can only activate B cells with the help of helper T cells, exhibiting the need for the cooperation between T and B cells for an effective immune response. Antigens that have such a complex, three-dimensional structure are more potent and capable of stimulating both humoral and cellular immune defenses compared to less complex molecules like carbohydrates, lipids, or nucleic acids.
To address part of the background information provided, antigen-presenting molecules found on all nucleated cells are MHC I molecules, and the TCR of a helper T cell binds to antigens presented with MHC II molecules. Antigens must be presented to T cells in the context of MHC molecules, and their complex structures are essential for T cell receptors and antibodies to recognize and bind them, with the potential to activate the adaptive immune response.