Human T and B lymphoid cells: an electron microscopic study on thymocytes, peripheral blood lymphocytes,...

Human lymphoid cells were studied by electron microscopy to find any morphological difference between T and B cells. The T cell population generally contains a smaller amount of the rough endoplasmic reticulum than the B cell in various functional states, i.e. peripheral blood lymphocytes of normal individuals, mitogen-stimulated lymphoblasts and lymphoid cell lines. This may depend on greater need of the rough endoplasmic reticulum for immunoglobulin synthesis in B cells, even though T cells produced some soluble mediators. Other differences between T and B cells are as follows: (1) Peripheral blood T lymphocytes often have clustered dense granules, while granules containing parallel tubular structures are more frequently seen in B lymphocytes. (2) Cultured T cell lines usually exhibit a higher nuclear-cytoplasmic ratio and less prominent nucleoli than B cell lines.