An immortalized cell line is called “immortal” because it can keep dividing in the lab for a very long time. The cells skip normal cell senescence. In contrast, most primary cells have a built-in limit to how many times they can divide. This happens because of something called telomeres, which are protective caps at the ends of chromosomes. Every time a cell divides, these telomeres get a little shorter, and eventually, the cell stops dividing altogether.

Human dermal fibroblasts are widely used for various in-vitro research in the laboratory. The cells are used for the purpose of various skin biology studies including cell signaling, disease modeling, diagnosis, and therapeutics. These cells play an important role in maintaining skin structure by producing collagen and other support proteins, which makes them useful for studying how skin repairs and heals after injury.
Scientists use fibroblast cells for a detailed understanding of how cells grow, communicate, signal, and respond to different conditions/stimuli. For example, they can observe how these cells react to stress, inflammation, or new drug compounds. This helps researchers get an early idea of whether a treatment might be safe or effective.

Adipose-derived stem cells (ADSCs) refer to heterogeneous populations of stem and progenitor cells that are isolated from adipose or fat tissue. The isolation of the ADSCs involves minimally invasive procedures such as liposuction or small-section incision. The isolated cells are key components of stromal vascular fraction (SVF), which is isolated after enzymatic digestion or mechanical processing of adipose tissue.
ADSCs primarily include mesenchymal stem cells (MSCs) that have regenerative potential. MSCs possess the unique ability to differentiate into various adult cell lineages. These include adipogenic (fat), chondrogenic (cartilage), osteogenic (bone), and tendons.

Endothelial cells are specialized cells that form the inner lining of blood vessels and lymphatic vessels. Morphologically, endothelial cells are flattened cells that are selectively permeable. These cells form a barrier between the blood and its surrounding tissues. This maintains vascular homeostasis.
Structurally, endothelial cells are tightly connected by junction proteins. These regulates cellular permeability. This enables the exchange of adequate oxygen, nutritional supply, hormones, and the removal of metabolic waste. These cells act as passive barriers as well as metabolically active elements that participate in numerous physiological processes.

Alveolar macrophages in the lungs are specialised cells that are present in the epithelial surface of alveoli. This is the site where gaseous exchange is facilitated. These macrophages serve as the first line of defence in the respiratory system. These cells conduct surveillance of inhaled air for pathogens, allergens, particulate matter and environmental pollutants.
It is involved in phagocytosis of foreign particles- the process of engulfing and digestion of microorganisms, debris and dead cells. It efficiently clears bacteria, viruses, fungal spores, and particulate matter. Alveolar macrophages further maintain sterility in the lower respiratory tract and further prevent infection.