Ultrastructure of Rosette-Forming Cells in the Mouse during the Antibody Response

Abstract

Ninety-four single rosette-forming (RF) cells obtained from the spleens of mice 2 to 6 days after primary injection of sheep erythrocytes were studied with the electron microscope. The observed RF cells could be classified in five ultrastructurally distinct groups, 1) lymphocytes, 2) plasma cells, 3) “cells with pale nuclei,” 4) “cells with cytoplasmic bodies,” and 5) macrophages. Two morphologic findings had not been described in antibody-containing cells before. 1) In most of the medium-sized and in all the large RF lymphocytes clusters of ribosomes were surrounded by patches of matrix more electron dense than the rest of the ground substance and less dense than the ribosomes. The significance of these patches with respect to antibody synthesis is discussed. 2) Cells in Group 4 contained round lysosome-like cytoplasmic bodies, which were larger (τ;2 µ diameter) than the lysosomes described in lymphoid cells transformed by mitogens. The cytoplasm of some of these cells was otherwise undifferentiated. The developmental interrelations of the various RF cells are discussed in terms of morphologic criteria and sequence of appearance.