In vivo maturation of B cells in the spleen of nude mice following administration of bacterial lipopolysaccharide.

Morphological changes of the splenic white pulp in athymic nude mice (nu/nu) and their normal littermates (nu/ + ) following intraperitoneal injection of bacterial lipopolysaccharide were studied by light and electron microscopy, immunofluorescence and autoradiography. Early blast formation and subsequent appearance of IgM-containing cells were observed by 72 h and at 120 h, respectively, in the periarteriolar sheath of nu/nu mice and in the follicular area of nu/ + mice. Ultrastructural details of blasts and the time course of their development were similar in both nu/nu and nu/ + mice. Lymphoblasts showed a large nucleus with a prominent nucleolus, many polysomes and poorly developed smooth endoplasmic reticulum. Plasmablasts had a nucleus with coarse heterochromatin and copious cytoplasm filled with dilated rough endoplasmic reticulum. Generally, lymphocytes proliferated and differentiated through lymphoblasts to plasmablasts by 72 h and finally to plasma cells at 120 h. However, this development was asynchronous since lymphoblasts, plasmablasts and plasma cells were observed simultaneously at 72 h. It was suggested that a B cell subset responsive to bacterial lipopolysaccharide matures to antibody-forming cells in the thymus-dependent area in nu/nu mice and in the thymus-independent area in nu/ + mice.