Coupe d’un tube séminifère de testicule de souris
Section of a seminiferous tubule from a mouse testis measuring 20 µm thick, observed using a multicolour confocal microscope. The heads of the spermatozoa have been labelled in red using immunofluorescence (phalloidin labelled with the fluorochrome Alexa-647), while their tails are shown in cyan (DAPI). Testicular macrophages are mobilised to defend the spermatozoa. By emitting specific molecules, these fertility guardians prevent other elements in the immune system entering the testes. A recent study made it possible to characterise the two types of testicular macrophage and find out about the origin, development and characteristics of these immune cells. The first type of testicular macrophage is of embryonic origin, while the peritubular macrophages are located around the seminiferous tubules. By using a new cell tracing method, researchers were able to follow the peritubular macrophages (from the bone marrow to the testes), which only appear two weeks after the mice are born, the stage that corresponds to puberty in humans. Surprisingly, once established in the testes, both macrophage populations remain there for the rest of their lives. This discovery could lead to the development of new treatments for male infertility. In confocal microscopy, the technique used to produce this image, the sample is scanned by laser beams, point by point. This produces fine optical sections that reveal the location of numerous entities or cell types (T cells, B cells, dendritic cells, macrophages, actin, nucleus, etc.) in a section of tissue. In this way, research scientists can compare the number and location of entities in various situations, in individuals affected by pathologies, for example, in order to decipher the mechanisms of the immune system. This technique, used commonly in laboratories, is improving all the time in terms of the resolution, sensitivity, colours and contrasts possible.