Final answer:
The major battleground for HIV and the immune system occurs mainly in the lymph nodes, which are a component of the systemic immune system.
Step-by-step explanation:
The major battleground for HIV and the immune system takes place in the lymph nodes. Lymph nodes are part of the systemic immune system, which works in conjunction with the mucosal immune system. The mucosal immune system is primarily constituted by Mucosa-associated lymphoid tissue (MALT), which provides the first line of defense against pathogens at mucosal surfaces. MALT encompasses various parts of the body such as the nasal passages, mouth, pharynx, esophagus, gastrointestinal tract, respiratory tract, and urogenital tract. HIV, however, mostly targets T cells found in lymphoid tissues like lymph nodes, eventually causing a decline in the immune system's ability to fight off infections and diseases.