Leukocyte trafficking in the efferent lymph of pigs – confirmation and extension of earlier observations

Pig models are employed widely in burns research and xenotransplantation, yet the physiological characteristics of efferent lymph under stable baseline conditions remain incompletely defined. A key unresolved issue is whether detectable leukocytes persist in peripheral efferent lymph under sustained RBC-free (red blood cell-free) collection conditions, beyond the surgically confounded conditions reported in earlier studies. Earlier reports of lymphocyte recovery were frequently confounded by RBC contamination, suggesting tissue injury or collection before restoration of physiological homeostasis. In this study, efferent lymph was successfully collected from the mammary (superficial inguinal) lymph nodes of pigs for over two weeks. In samples consistently free of RBCs, no leukocytes were detected, and no coagulation occurred even without anticoagulants. In contrast, ovine efferent lymph collected under equivalent conditions clotted readily in the absence of anticoagulants. These findings confirm and extend earlier observations on the cellular and haemostatic properties of porcine efferent lymph and support a practical operational definition of physiological lymph as sustained RBC-free lymph collected over consecutive days. The results further highlight species-specific differences in immune cell trafficking and clotting dynamics relevant to burn models and xenotransplantation research.