The development of IgM- and IgG-containing plasmablasts in the white pulp of the spleen after stimulation with a thymus-independent antigen (LPS) and a thymus-dependent antigen (SRBC).

This study describes the development of IgM and IgG containing plasmablasts in splenic white pulp after a single intravenous injection of the thymus-independent antigen lipopolysaccharide (LPS) or the thymus-dependent antigen sheep erythrocytes (SRBC) using immunohistoperoxidase techniques. Attention has been paid especially to the sites where IgM and IgG blasts develop in the white pulp and their migration route, from the white pulp towards the red pulp. The distribution of IgM and IgG blasts in the different white pulp compartments, i.e. outer periarteriolar lymphocytic sheath (PALS), inner PALS, follicles and the area along the terminal arteriolar branches, has been studied. Our findings indicate that both the thymus-independent IgM response to LPS and the thymus-dependent IgM response to SRBC start in the outer PALS. During the course of the immune response against SRBC the early localization of IgG plasmablasts in the white pulp was dispersed through the whole PALS. Later in the immune response the IgG blasts in the white pulp were localized especially in and at the border of follicle centres. No significant development of IgG blasts was found after LPS administration. The results of the present study suggest that during the immune response the bulk of IgM blasts migrates via the outer PALS and along the terminal arteriolar branches into the red pulp.