Mechanism of follicular trapping: similarities and differences in trapping of antibody-complexed antigens and carbon particles in the follicles of the spleen.

Both immune complexes and carbon particles were trapped in spleen follicles soon after intravenous injection. The localization pattern of carbon particles and immune complexes were identical 24 hr after injection. Since there is no reason to believe that lymphocytes are involved in the transport of carbon particles from the marginal zone towards the follicle centers, these results indicate that follicular trapping is based on a purely mechanical process. Pretreatment with endotoxin completely prevented the trapping of immune complexes but not carbon particles. Endotoxin administered after the injection of immune complexes caused the rapid removal of trapped complexes from the follicles. However, the effect of endotoxin on trapped carbon particles was less pronounced. Apart from a mechanical trapping of diffusing compounds in the follicular web, a distinct phase is suggested in which immune complexes are fixed to and retained on the surface of the follicular dendritic cells.