Abstract
Plasma cells (PCs) in human palatine tonsils are predominantly located in the germinal centres (GCs), in the subepithelial space and near the deep connective tissue septa surrounding each crypt. We analysed the location, phenotype, and proliferation of GC PCs by immunohistology comparing them to PCs in the other two locations. Most PCs in GCs were strongly positive for CD38, CD138, CD27, IRF4, and intracellular (ic) IgG. They often accumulated in the basal light zone, but could also be found scattered in the entire light zone. In addition, rows of PCs occurred at the surface of the GC bordering the mantle zone, i.e., in the outer zone, and at the surface of the dark zone. The latter cells were often continuous with PCs in the extrafollicular area. The vast majority of GC PCs were negative for Ki-67. Only a few Ki-67+ plasmablasts, predominantly icIgG+ or icIgM+, were found inside GCs. In certain GCs PCs accumulated around capillaries and the adjacent perikarya of follicular dendritic cells (FDCs). Newly formed PCs might migrate from the basal to the superficial part of the light zone and then back to the dark zone surface to leave the GC. This guarantees an even distribution of secreted Ig for exchange with immune complexes on FDCs. The surface of the dark zone may also be an exit site for Ki-67+CD30+ B lymphoblasts, which seed perifollicular and extrafollicular sites. We speculate that these cells tend to downmodulate CD20 and activation-induced deaminase and further up-regulate CD30 when developing into pre-plasmablasts.
Highlights
Plasma cells (PCs) have been known as regular and potentially abundant constituents of secondary follicles in human tonsils and in the lymphatic organs of experimental animals for about 50 years (Lennert et al 1967; Curran and Jones 1977; Korsrud and Brandtzaeg 1980; Nieuwenhuis and Opstelten 1984; Arpin et al 1998)
The overall structure of tonsils was first visualised by double-staining B and T lymphocytes for CD20 and CD3, respectively (Fig. 1a)
The results reported in this study show that large numbers of PCs are present in special areas of human tonsil germinal centres (GCs)
Summary
PCs have been known as regular and potentially abundant constituents of secondary follicles in human tonsils and in the lymphatic organs of experimental animals for about 50 years (Lennert et al 1967; Curran and Jones 1977; Korsrud and Brandtzaeg 1980; Nieuwenhuis and Opstelten 1984; Arpin et al 1998). It is likely that GCs in humans and especially in tonsils are, long-lasting. Tonsils are permanently confronted with materials of viral, bacterial, and fungal origin in the oral and nasal cavity. Their GCs are most probably established by a large number of different B-cell clones responding to various antigenic molecules and to different epitopes in single antigens (Mesin et al 2016; Küppers et al 1993). Tonsils are only removed if long-term— perhaps even overshooting—B-cell reactions provoke recurrent inflammation or spatial obstruction. Tonsils are ideal for observing human B cells and plasma cells during long-lasting immune responses of high intensity. Tonsils do not occur in mice or rats, which means that immunological
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
