Phagocytosis and macropinocytosis are crucial cellular processes involved in engulfing and internalizing particles. Phagocytosis is specific, involving the recognition and binding of target particles, while macropinocytosis is non-selective, allowing cells to internalize large volumes of fluid and nutrients. Both processes play key roles in immune response, nutrient acquisition, and cellular signaling.

Clathrin-coated pits and caveolae are distinct structures on the cell membrane with different functions in immunology. Clathrin-coated pits are involved in antigen uptake and processing by antigen-presenting cells, while caveolae regulate immune cell activation and cytokine production. Both structures play pivotal roles in immune surveillance and response to pathogens, influencing immune signaling pathways and inflammatory responses.

Pinocytosis, or "cell drinking," involves the uptake of small dissolved substances and fluids by cells. It's utilized by various cell types such as epithelial, white blood, and endothelial cells for nutrient intake, immune response, and substance regulation. Pinocytosis rates can change based on nutrient availability, signaling molecules, and the presence of pathogens or toxins. The process involves the fusion of pinocytic vesicles with endosomes, with cargo sorted for recycling or degradation within lysosomes.