At birth, human immune system differentiate between native cells pathogenic cells. But in males, sperm develop at puberty, the sperm may be recognized as foreign cells by some elements of the immune system.
Testicular macrophages are immune cells that rush to the defense of sperm. By releasing specific molecules, these guardians of fertility prevent other immune system agents from getting to the testes.
Macrophages migrate to sites of infection and phagocytose pathogens. They also modulate immune system activity to ensure proper organ function and regeneration.
They may arise from embryonic progenitors or bone marrow cells in adults. The testis is divided into two compartments; one of testicular macrophage is in the interstitial spaces, where testosterone-producing Leydig cells are located.
These interstitial macrophages are of embryonic origin: they are present at birth. The other is peritubular – it is located on the surface of the seminiferous tubules that house sperm cell precursors.
Each macrophage population has distinctive cellular markers. The researchers used a new cell tracing method to follow the movement of peritubular macrophages from the bone marrow to the testes in mice.
They discovered that these macrophages only appear two weeks after the birth of mice, the same duration in human. Once they have been established in the testes, macrophages remain there for the rest of their lives.