Morphological changes in the mouse popliteal lymph node after local injection of dextran sulfate.

Dextran sulfate 500 (DS) is known to be a potent B-cell mitogen. Injection of this compound (500 micrograms) into the footpads of mice produced characteristic changes in the draining popliteal lymph nodes, including elimination of macrophages from the lymphatic sinuses and lining the subcapsular sinus, a marked blast reaction throughout the nodal parenchyma, damage to the stroma of the outer peripheral cortex, and disorganization of all the existing primary and secondary lymph follicles. On day 6 after DS treatment, small lymphocytes bearing surface Ig were detected and distributed loosely and broadly in the deeper part of the peripheral cortex without any tendency to reorganize lymph follicles. On day 21, these small lymphocytes populated the outer and deeper layer of the peripheral cortex, sometimes forming nodular accumulations representing regenerating lymph follicles, and on day 35, various numbers of regenerated lymph follicles were present in the peripheral cortex. Tracer studies using FITC-conjugated human serum albumin showed that intraparenchymal diffusion of labeled HSA was highly blocked at the outer peripheral cortex on days 4 through 14, and that this pathway began to reopen at around 21 days. Disorganization of lymph follicles could be considered due to extensive damage to follicle stromata which became unable to bind B lymphocytes, and follicles seem to be re-organized in response to lymph-carried antigen in addition to restored follicle stromata and repopulation B lymphocytes. Macrophages had little effect on the lymph follicle formation in this study.