Human spleen microanatomy: why mice do not suffice

Abstract

SummaryThe microanatomical structure of the spleen has been primarily described in mice and rats. This leads to terminological problems with respect to humans and their species-specific splenic microstructure. In mice, rats and humans the spleen consists of the white pulp embedded in the red pulp. In the white pulp, T and B lymphocytes form accumulations, the periarteriolar lymphatic sheaths and the follicles, located around intermediate-sized arterial vessels, the central arteries. The red pulp is a reticular connective tissue containing all types of blood cells. The spleen of mice and rats exhibits an additional well-delineated B-cell compartment, the marginal zone, between white and red pulp. This area is, however, absent in human spleen. Human splenic secondary follicles comprise three zones: a germinal centre, a mantle zone and a superficial zone. In humans, arterioles and sheathed capillaries in the red pulp are surrounded by lymphocytes, especially by B cells. Human sheathed capillaries are related to the splenic ellipsoids of most other vertebrates. Such vessels are lacking in rats or mice, which form an evolutionary exception. Capillary sheaths are composed of endothelial cells, pericytes, special stromal sheath cells, macrophages and B lymphocytes. Human spleens most probably host a totally open circulation system, as connections from capillaries to sinuses were not found in the red pulp. Three stromal cell types of different phenotype and location occur in the human white pulp. Splenic white and red pulp structure is reviewed in rats, mice and humans to encourage further investigations on lymphocyte recirculation through the spleen.

Elasticity mapping of murine abdominal organsin vivousing harmonic motion imaging (HMI)

“…Small animal studies measuring stiffness in different abdominal organs are lacking. Literature does exist in big animals and patients, but comparison with our results is limited because of the differences in organ structure (Dolenšek et al 2015; Steiniger 2015). Moreover, definite conclusions on healthy abdominal organs relative stiffness remains to be determined.…”

Germinal Center Hypoxia Potentiates Immunoglobulin Class Switch Recombination

“…While such examples exist, the GC is generally considered to be the “professional” site of CSR and SHM, and perhaps the hypoxic microenvironment within the GC helps promote this. In line with this thinking is the curious observation that while human GCs can be somewhat larger than murine GCs (25), many are the same size (26, 27)(and personal communication with G. Kelsoe), lie toward the center of the follicle (28), have been shown to express HIF-1α and are poorly vascularized (7). The development of hypoxia within the GC also raises the question if this hypoxic microenvironment is sufficient to drive neovascularization of secondary follicles over the course of a GC reaction.…”

Emergence and Evolution of Secondary Lymphoid Organs

“…Differences in the microarchitecture of the WP have been observed not only among different mouse species, but also within Mus musculus (A. Thiriot, personal communication). The architecture of human WP differs from that of mouse WP as well (Mebius & Kraal 2005, Steiniger 2015), although the characteristics that separate human WP from its evolutionary precursors remain poorly studied (see below). Moreover, the ontogeny of human WP differs from that of mouse WP: Ontogeny begins in utero, although its onset is still marked by the perivascular accumulation of B cells (Steiniger et al 2007).…”