Effect of sublethal X-irradiation on follicular trapping of immune complexes in the mouse lymph node

In one set of experiments, the effect of sublethal X-irradiation on the 24 h localization of subcutaneously injected immune complexes in the lymph node follicles was studied in mice which were given HRP-anti-HRP complexes into the rear footpad at 1-3 weeks after irradiation and killed 1 day later. The 24 h follicular localization of injected immune complexes in draining popliteal nodes was severely impaired at 7 days after irradiation, at which time residual follicles were markedly depleted of B lymphocytes. In following weeks, residual follicles began to be repopulated, and the 24 h follicular localization of immune complexes became restored. Follicular dendritic cells (FDC), as was detected by the in vitro trapping assay and/or by the immunostaining for complement receptors CR1, were present in lymph nodes at any time after irradiation. Another group of mice were given HRP-anti-HRP complexes at 6 days of X-irradiation and killed from 15 min to 24 h later. Following the injection, complexes localized in residual follicles in draining nodes within 15 min but soon diminished in density and finally disappeared by 24 h after injection. It is obvious that sublethal irradiation affect neither transport of immune complexes to lymph node follicles nor their localization in these follicles. Rather rapid disappearance after temporal localization of immune complexes in residual follicles irradiated mice indicates that persisting FDC were unable effectively to trap immune complexes which were transported and localized in residual follicles. Ineffective trapping by FDC of immune complexes temporally localized in residual follicles is discussed in relation to the depletion of follicular B lymphocytes due to X-irradiation.