Core Framework & Diagram Macrophages: The Cleanup Crew

One core reason is the difficulty of reversing macrophage M1 state. In a chronic inflammatory environment, continuous pro-inflammatory signals (from tissue damage, adipocytes, and senescent cell SASP) keep pushing macrophages toward M1 state, while M1 macrophages themselves secrete pro-inflammatory cytokines that form a positive feedback loop maintaining this activated state. Breaking this cycle requires eliminating the fundamental drivers of chronic inflammation (reducing visceral fat, improving sleep, controlling chronic stress) — not just pharmacologically suppressing symptoms.

Checkpoint therapy primarily targets T cells (lifting T cell exhaustion), but macrophages are also involved. PD-L1 (the target of PD-1 inhibitors) is expressed not only on tumor cells but abundantly on TAMs. TAMs suppress T cells through PD-L1, so PD-1/PD-L1 inhibitors simultaneously lift TAM-mediated T cell suppression. This explains why TAM density and type in the tumor microenvironment influences checkpoint therapy outcomes.

Alzheimer's disease is closely linked to chronic microglial (brain macrophage) activation. Amyloid-β plaques in Alzheimer's brains activate microglia into an M1-like state, continuously releasing pro-inflammatory cytokines that accelerate neuronal damage and synaptic loss. Multiple Alzheimer's studies targeting neuroinflammation and microglial function regulation are underway — one of the most active research directions in the field.

In fatty liver (particularly non-alcoholic fatty liver disease, NAFLD), liver Kupffer cells are persistently activated by fatty acids and endotoxins (LPS from the gut, increased through leaky gut) into an M1 pro-inflammatory state, secreting large amounts of TNF-α and IL-1β that drive hepatic inflammation. Without intervention, this can progress to non-alcoholic steatohepatitis (NASH), then to fibrosis and cirrhosis. Reducing visceral fat (weight loss) and improving gut barrier function (high-fiber diet, probiotics) are the key intervention points for interrupting this inflammatory cascade.