Macrophagia

Macrophages recognize and engulf bacteria using specialized receptors that detect pathogen-associated molecular patterns (PAMPs) on microbial surfaces—such as lipopolysaccharides on Gram-negative bacteria or peptidoglycan on Gram-positive bacteria—through pattern recognition receptors (PRRs) like Toll-like receptors (TLRs) and C-type lectin receptors (CLRs).

When a PRR binds to its corresponding PAMP, it triggers intracellular signaling cascades that activate the macrophage, inducing phagocytosis in which the bacterium is engulfed into a phagosome.

This phagosome then fuses with lysosomes to form a phagolysosome, where hydrolytic enzymes and reactive oxygen/nitrogen species degrade the pathogen.

Simultaneously, PRR signaling upregulates cytokine production to recruit other immune cells, amplifying the inflammatory response.