Phenotypic identification and development of distinct microvascular compartments in the postnatal mouse spleen

In this paper we report the development of the sinus network of mouse spleen during the first postnatal month as studied with a set of new rat monoclonal antibodies (mAbs) against mouse splenic endothelial cell subpopulations. One of the new mAbs (IBL-7/1) also stained B-cell lineage cells in the spleen shortly after the birth as confirmed by three-color flow cytometry. This B-cell staining in the primordial follicles vanished by the fourth postnatal week, so that the expression of IBL-7/1 antigen was restricted to the marginal sinus endothelium and some red pulp sinuses and a minor B-cell subset in the spleen, presumably distinct from the follicular B-cell compartment. The other mAb (IBL-9/2) selectively labeled the sinusoids of the deeper part of the red pulp, without any reactivity against hemopoietic cells. The IBL-9/2-reactive cells in newborns appeared as isolated elements throughout spleen, and during the segregation of white and red pulps they formed an extensive network in the red pulp outside the marginal zone. Double-labeling immunofluorescence revealed that most of these sinusoids also stained weakly with IBL-7/1 mAb, whereas the strongly IBL-7/1-positive vessels of this region were IBL-9/2 negative. Neither of these mAbs reacted with the central artery. The comparative phenotypic analysis of the various vascular segments indicates that the splenic sinusoids of the marginal zone and red pulp, respectively, are lined with a heterogeneous array of endothelium. For the precise identification, isolation, and characterization of the possible homing function of these endothelium subsets these region-specific mAbs may be of potential value.