Afferent lymph and lymph borne cells: their influence on lymph node function.

In AO rats the afferent lymphatics to the right cervical lymph nodes (LN) were interrupted and the LN were encased in silicone rubber tubes to prevent reunion of the lymphatics. At regular intervals over the next 12 weeks the following were measured in comparison with the intact contralateral LN - LN weight, influx of lymphocytes from the blood, blood flow, the incorporation of 125IUdR and the incorporation of 35S-sulphate into high endothelial venules (HEV). Systematic histological observations are also reported. One day after deafferentization lymphocyte influx was significantly reduced although blood flow was unchanged and a temporary increase in LN weight was associated with crowding of the lymphatic sinuses with small lymphocytes. The subsequent decline in lymphocyte influx was biphasic and quicker than the decline of other parameters--being undetectable by 6 weeks. Flattening of HEV and diminished secretion of 35S-sulphate was noted at 1 week and progressive degeneration and eventual disappearance of the HEV network was seen by 6-12 weeks. Doubtlessly because of lack of antigenic stimulation 125IUdR incorporation, and numbers of lymphoblasts, plasma cells and finally germinal centres were progressively reduced. The numbers of macrophages and interdigitating cells (IDC) were greatly reduced by 3 weeks and very few were present at 6 weeks probably because most or all arrive in afferent lymph and have a limited life span in the LN. At 12 weeks the LN was difficult to recognize as such since only stromal cells and occasional small lymphocytes remained. In supplementary experiments u.v. irradiation of the LN at the time of deafferentization reduced lymphocyte influx without affecting blood flow suggesting that a u.v. sensitive cell like the IDC may influence lymphocyte influx. In conclusion the involution of the deafferentized LN is partly due to the lack of antigen but progression to the complete loss of specialized structure and function is probably due to lack of other factors including non-lymphoid cells that normally arrive in afferent lymph.