Immunospecific labeling of mouse lymphocytes in the scanning electron microscope

Bone marrow-derived (B) and thymus-derived (T) Balb/c mouse lymphocytes were identified in the scanning electron microscope (SEM) by the immunospecific attachment of one of several kinds of large-molecular-weight markers distinguishable in SEM. These markers (tobacco mosaic virus, keyhole limpet hemocyanin, bushy stunt virus, and bacteriophage T4) could be modified with hapten groups and linked with anti-hapten antibody, in an indirect (sandwich) scheme, to hapten-modified anti-cell-surface antibody bound to the cell surface. Hapten-modified antibodies to B cell antigens (goat anti-mouse-immunoglobulin) or to T cell antigens (rabbit anti-mouse brain) were employed to identify these two lymphoid cell types in unfractionated spleen, mesenteric lymph node, bone marrow, and thymus cell populations. The topography of B cells was always indistinguishable from that of T cells. No surface features were found to be unique to either cell type. In suspension, the majority of B and T cells had one or no microvilli regardless of the tissue source of the labeled cells. Cells in suspension that had microvilli (usually 10% of the total cell population) were always unlabeled. However, after cell contact with a glass surface, approximately half of both the B and T cell population had a villous topography.