Final answer:
Both IgG1 and IgG3 are antibodies that play a direct role in opsonization by marking pathogens for enhanced phagocytosis, whereas IgD does not participate in this process.
Step-by-step explanation:
The question asks which among the listed antibodies are involved in opsonization, a process where pathogens are marked and coated to enhance phagocytosis by phagocytic cells. Among the options given, IgG1 and IgG3 are the antibodies involved in opsonization. These antibodies bind their Fab sites to pathogens and present their Fc portion to phagocytic cells, such as macrophages and neutrophils, facilitating the phagocytosis of the pathogens.
In contrast, IgD does not play a direct role in opsonization. Thus the antibodies involved are both IgG1 and IgG3, making the correct answer 'Only IgG1 and IgG3.'