Individual variation in and lateral asymmetry of mouse epididymal draining lymph nodes

Draining lymph nodes (LNs) are pivotal sites for maintaining tolerance to self-antigens as well as eliciting immune responses to exogenous antigens. The epididymis is a male reproductive organ with a unique local immune environment. Although mice are the most commonly used laboratory animals for immunology research, there are no detailed descriptions of the anatomical location and function of LNs that drain the epididymis.Evans blue labeling was utilized to explore lymphatic drainage of the epididymis in eight- to ten-week-old male C57BL/6 mice. We confirmed the lymphatic drainage of the epididymis in mice using the objective technique of carboxyfluorescein succinimidyl ester (CFSE)-labeled cells.By combined Evans blue labeling and fluorescent labeling, we found that 1) the patterns of epididymal LN drainage are highly heterogeneous between individual mice; 2) the leftside LNs participate in drainage more frequently than the right-side LNs; and 3) epididymal lymphatic drainage bypasses both the paraaortic and renal LNs in some mice.These data highlighted the need to consider the individual variation in and lateral asymmetry of draining LNs when characterizing the regional immunology of the mouse epididymis.