5. Immune System Response
Macrophages and Phagocytosis
The body's innate defense mechanisms emerge when semi-permanent makeup pigment is introduced, treating it as a foreign entity. Non-specific immune cells rush to the site, including macrophages, histiocytes, and neutrophils. Macrophages, capable of consuming particles up to 10 micrometers, engulf common pigment particles about 500 nm in diameter through phagocytosis. Some macrophages die and become permanent pigment holders within the dermal layer.
Specialized Immunity
As the immune response evolves, specific immunity with T-lymphocytes and B-lymphocytes plays a role. T-lymphocytes target and destroy cells with foreign antigens, while B-lymphocytes might produce antibodies to neutralize the pigment, although this is less common in semi-permanent makeup.
Pigment in the Lymphatic System
Some pigment particles end up in the lymph nodes, where they typically remain indefinitely, as lymph nodes can't expel or break down these materials. This is why ink particles are sometimes found during autopsies.
Note on Macrophage Lifespan
Macrophages have varying lifespans, from days to months, influenced by the tissue environment and activation state. However, they are continually regenerated from bone marrow precursors, maintaining a dynamic but persistent role in pigment retention.
Transfer to the Lymphatic System
Some believe that iron oxide particles are transferred to lymph vessels, especially when one macrophage dies and releases the particle, and another isn't immediately ready to engulf it. This removal process contributes to the persistence of pigment in the skin, which depends on its chemical composition and the immune system's intricate workings.
Pigment Encapsulated in Fibroblasts
After application, pigment molecules cluster and are gradually surrounded by fibroblasts, which transform into myofibroblasts during the skin's healing response. These cells move toward the pigment, secreting structural proteins like collagen to form a fibrotic capsule, isolating and protecting the pigment. However, this encapsulation can remodel over time, affecting the pigment's appearance.
Pigment Stabilization in the Extracellular Matrix (ECM)
Pigment particles also settle into the skin's ECM, a complex structure supporting and sometimes ensnaring the pigment through physical adsorption, mechanical interlocking, and biochemical anchoring. After pigmentation, the ECM might increase its matrix around the pigment, enhancing stability and resistance to the immune response. These processes contribute to the pigment's longevity and stability in the skin.