Cytometric analysis of small lymphocytes in the bone marrow and lymphatic tissues in neonatally thymectomized and nude mice, with particular reference to differentiation of B-lymphocytes.

In neonatally thymectomized mice and nude mice, small lymphocytes in the bone marrow, Peyer's patches, lymph nodes and spleen were studied qualitatively and quantitatively by electron microscopy. Marrow lymphocytes which are mostly small lymphocytes are classified into dark and light types. The greater proportion of marrow small lymphocytes are of the dark type. Small lymphocytes in Peyer's patches, lymph nodes and spleen are of the light type. The nuclear and cellular sizes of small lymphocytes were estimated stereologically. The nucleus-cell ratio, the volumetric proportions of mitochondria, Golgi apparatus, tubular complexes and dense bodies to the cell body and the proportions of nucleoli and nuclear bodies to the nucleus were also determined. The quantitative results thus obtained suggest that light small lymphocytes in the bone marrow are cytometrically similar to small lymphocytes in Peyer's patches, lymph nodes and spleen and that dark small lymphocytes in the bone marrow are different from other small lymphocytes. The findings are discussed in particular relation to morphological differentiation of B-lymphocytes.