II. Ultrastructural differences in attachment patterns of indicator cells to target cells in the rosette-forming process.

A comparison was made of the electron microscopic appearances of rosettes formed between mouse spleen lymphocytes and indicator cells with the ligands exposed on their surfaces either in clusters or in continuity. Sheep red blood cells (SRBC) coated with protein A of Staphylococcus aureus or human IgG by the chromium chloride technique were used as indicator cells with cluster distribution of the ligand. RBC coated with rabbit IgG anti-sheep red blood cells or staphylococci were used as indicator cells with uniform distribution of the ligand. Results show that the appearance of the zones of contact (point attachment or broad zone attachment) between lymphocytes and indicator cells are mainly influenced by the distribution of the specific ligands on the surface of the indicator cells and do not reflect the pattern of distribution of receptors on lymphocytes.