In the testicles, macrophages are guardians of fertility

Two types of testicular macrophages have recently been characterized by CNRS researchers at the Marseille-Luminy Immunology Center (CNRS / Inserm / Aix-Marseille University). A novel method of cellular tracing has enabled them to establish the origin, the development and the characteristics of these immune cells. This fundamental discovery is promising to understand some cases of infertility in men and to consider new treatments.
From the beginning of the individual’s life, the immune system learns to differentiate the cells belonging to the organism – the self – from other potentially pathogenic cells. However, since spermatozoa appear only at puberty, they are likely to be identified as foreign to the organism by some actors of the immune system. Special cells of the immunity, the testicular macrophages, are then mobilized to defend the spermatozoa. By emitting specific molecules, these fertility guardians prevent other actors of the immune system from entering the testicles.
If they are able to infiltrate infectious sites to phagocytate and destroy pathogens, Macrophages can also modulate the activity of the immune system to protect the functioning and regeneration of organs. These cells of immunity may be of embryonic origin or develop in the bone marrow in adults. Michael Sieweke’s team at the Marseille-Luminy Immunology Center (CNRS / Inserm / Aix Marseille University) was able to determine the profile of the two types of testicular macrophages.
The testicle is divided into two compartments. The first type of testicular macrophage described by the researchers is in the interstitial compartment, which also includes testosterone producing cells. The origin of these macrophages is embryonic: they are therefore present from the beginning of the life of the individual. The peritubular macrophages are located in the tubular compartment, around the seminiferous tubes which house the precursors of the spermatozoa. These two populations of macrophages have different cell markers.
Using a novel method of cell tracing, the researchers were able to follow the peritubular macrophages from the bone marrow into the testicles. The results showed that this type of macrophages only appeared two weeks after the birth of the mice, the equivalent of puberty in humans. Surprisingly, once established in the testes, the two populations of macrophages remain there all their lives.

CNRS
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