Seasonal features of lymphocyte extravasation through the lymph nodal HEVs (Bats)

Introduction. Given the importance of lymphocyte homing m immune response it was studied the lymphocyte extravasation through the HEVs in lymph node in 12 hibernating animals. Materials and Metods. We used lymph nodes of bats captured in the years 1972- 1980: five female bats were captured during dormancy of the winter months (from December to February) and 7 female bats captured during summer months (July and August). The lymph nodes were fixed in osmic acid 1% in veronal buffer, dehydrated with acetone and embedded in Durcupan; semithin and serial ultrathin sections were stained with 0,5 % Toluidine blue and lead citrale according to Reynoids, respectively, and observed by transmission electron microscope. Results and conclusion. The HEVs of the cortical and paracortical area of the lymph node in bats captured from July to August display many lymphocytes englobed in the endothelial wall, which is characterized by high endothelial cells. The heterogeneous morphological features of this lymphocytes, during the different moments of the extravasation process, should be attributed to the distinctive moment of the transmigratory process, as well as the casual direction of the section plane. The presence of lymphocytes into the HEVs of the lymph nodes excised during the months from December to February is rather limited. The ultrastructural features of lymphocytes during transmigration is limited too. In either season, dormancy and summer, the extravasation of the lymphocyte from blood circulation into the extravasal lymphoid matrix take place through an intraendothelial canalicular formation, as shown in the sequence of the serial ultrathin sections and from their three-dimensional reconstruction. The numerical density of the ultrastructural features displaying seasonal lymphocyte transmigration through the endothelium of the HEVs is very limited during the dormant fasting, compared to the rather high density found in summertime, in dose relation to the seasonal changes in metabolic rate of the hibernating animal.