Final answer:
TH1 cells activate macrophages through two signals: antigen presentation via MHC II on APCs and secretion of cytokines like IFN-γ. These cytokines enhance macrophage's ability to destroy pathogens and contribute to the activation of other immune cells.
Step-by-step explanation:
The activation of macrophages by TH1 cells is essential for combatting certain intracellular pathogens and it requires two main signals. The first signal involves the presentation of antigens by Major Histocompatibility Complex class II (MHC II) molecules on the surface of antigen-presenting cells (APC), such as macrophages, to the TH1 cells. The second signal comprises of various cytokines secreted by TH1 cells that provide feedback to the macrophages and enhance their ability to ingest and destroy pathogens like Mycobacterium tuberculosis. These cytokines include interferon-gamma (IFN-γ), which is particularly important for the activation of macrophages.
In addition to their role in macrophage activation, TH1 cells help in stimulating cytotoxic T cells and may support their differentiation into memory cells. They also enhance the capability of neutrophils and Natural Killer (NK) cells. This TH1-mediated response is crucial for eliminating intracellular bacteria and may also participate in anti-tumor responses.