Tissue pool neutrophils of the bovine mammary gland: ultrastructural features during in vitro senescence

The aim of the study was to verify whether the in vitro senescence process of tissue pool neutrophils of the bovine mammary gland is accompanied by similar changes of ultrastructure as typically occurs in in vivo conditions. The experiments were carried out in four clinically healthy, Holstein x Bohemian Red-Pied crossbred heifers aged 14-16 months. With the aid of transmission electron microscopy (TEM), scanning electron microscopy (SEM) and flow cytometry (FCM), neutrophil apoptosis in vivo was detected and during senescence it was monitored in vitro. The neutrophil apoptosis comprised three ultrastructurally different stages: (1) karyopyknosis, (2) zeiosis, and (3) apoptotic bodies. These stages were obvious in the apoptotic neutrophils both in vivo and in vitro. In addition to the common morphological signs, however, ultrastructural differences were also detected in apoptotic neutrophils in vitro. These in vitro ultrastructural differences mostly comprised hyper-vacuolation of the cytoplasm with mega-vacuoles and secondary necrosis of apoptotic neutrophils. Morphological features of apoptosis during in vitro senescence of tissue pool neutrophils of the bovine mammary gland were shown to be in close accordance with these in vivo signs.