Identification and characterization of a novel CD2-positive cell population in the seminiferous tubule of Fischer CDF344 rats†

We report the presence of previously undocumented cell type in the spermatogonial stem cell niche expressing CD2 protein, using whole-mount immunofluorescence of rat seminiferous tubule preparations. Confocal imaging revealed CD2+ cells reside interspersed within the peritubular myoid cell (PTMC) layer surrounding the seminiferous tubules. Three-dimensional reconstruction and surface rendering models revealed cellular interaction between peritubular macrophages (PTMφs) and CD2+ cells. Mono-(2-ethylhexyl) phthalate (MEHP)-induced testicular injury model was utilized to investigate the dynamics of PTMφ-CD2+ cell interaction. Fischer CDF344 male rats were exposed to 700 mg/kg-bw MEHP or corn oil via oral gavage on postnatal day (PND) 28 and euthanized at 48 hours or 2 weeks post-exposure. In MEHP-exposed animals, a significant number of PTMφs encounter CD2+ cells at 48 hours post-exposure, suggesting it to be an adaptive response against the MEHP-induced toxicity. Moreover, neither the vehicle group (corn oil) nor the MEHP-exposed animals show a change in the temporal division dynamics of the CD2+ cells when followed along the acute (48 hours) and recovery (2 weeks) phases of post-injury, suggesting these cells as dormant cell population lacking susceptibility against MEHP-induced toxicity. Nevertheless, an increase in PTMφ-CD2+ cell interactions in response to testicular toxicity indicates a CD2+ cell-mediated link for dynamic intercellular communication between the innate immune cells and niche cells of the testis. This first report of the existence of a unique CD2+ cell population in the rat seminiferous tubules and their direct cellular interaction with PTMφs is anticipated to stimulate further research in the field of testicular immunobiology.