Lymphocyte capping and lymphocyte migration as associated events in the in vivo antigen trapping process. An electron-microscopic autoradiographic study in the spleen of mice.

The fate of 125I labeled antigen-antibody complexes in the first two hours after intravenous injection was followed in the spleen of mice by light and electron microscopic autoradiography. It appeared that AAC were phagocytized by granulocytes and by macrophages in the marginal zone and were present over the surface of lymphocytes in that area. By rinsing the spleen before fixation it could be shown that AAC were indeed bound to the lymphocyte membrane and not merely present in the blood plasma between the cells. The label was present in a spotty fashion or over a so-called uropod. The majority of labeled uropods (13 out of 17) pointed away from the follicle. From this it was inferred that these lymphocytes moved to and most probably into, the follicles. Inside the follicles, at 1 hour post injectionem, most of the label was associated with interfaces between lymphocytes. At 2 hours post injectionem there was a preferential localization over interfaces between lymphocytes and dendritic reticulum cells. It is conceivable that antigen that is introduced into the circulation is ultimately presented to dendritic reticulum cells in a complexed form with antibody, probably with complement, and with the B-cell receptor, since receptor shedding is a normal event following capping.