Search

The specialized M cells in the follicle-associated epithelium (FAE) of Peyer's patches (PP) represent an intimate interphase between luminal antigens and gut-associated lymphoid tissue (GALT). M cells form pockets that contain clusters of leucocytes probably involved in the first encounter with antigens from the gut lumen. Three-colour immunofluorescence in situ phenotyping of these leucocytes in humans revealed about equal numbers of B (CD19/20+) and T (CD3+) lymphocytes, the latter mainly CD4 + (median 73%, range 40-90%), but relatively few macrophages (CD68+). Most B cells (90%) were positive for surface IgM (sIgM) and often co-expressed sIgD (median 34%, range 6-60%). Occasional B cells (median 2%) did not express CD45RA (range 0-15%) and 13% virtually lacked HLA-DR (range 0-40%). Some B and T lymphocytes expressed the nuclear proliferation marker Ki-67 (range 1-10%). The M-cell pockets also contained occasional cells with cytoplasmic lgA or IgM. These sites thus contained a heterogeneous B-cell population with features of both follicular mantle (sIgD+ sIgM+) and marginal zone (sIgD- sIgM+) B lymphocytes. Adjacent T lymphocytes were generally of the memory phenotype (CD45RO+). Our findings suggest that the M-cell-associated B lymphocytes represent local extensions of B-cell follicles towards the gut lumen, developed topically to facilitate antigen presentation and diversification of mucosal immune responses. [ABSTRACT FROM AUTHOR]

Follicular dendritic cells (FDC) present in germinal centres trap considerable amounts of C3- containing immune complexes (IC). Activation of the terminal pathway of complement (C) on biological membranes normally generates C5b-9(m), which is the membranolytic form of the terminal complement complex (TCC). By contrast, when C activation takes place in the extracellular fluid phase, S-protein binds to C5b-7 and the non-lytic soluble SC5b-9 is formed. In this study deposits of C3d, C5, C9 TCC neocpitope and S-protein were demonstrated by immunohisto- chemistry on FDC in human tonsils, lymph nodes, spleens, appendices and colonic mucosae. TCC and S-protein were likewise observed on FDC in imprints from tonsils. The identical spatial distribution revealed by paired staining suggested that TCC had been generated in situ. The staining intensity for TCC and S-protein varied in parallel, which suggested that the S-protein may be incorporated in the membrane-bound TCC-perhaps rendering it non-lytic. However, the actual mechanism and function of the observed TCC and associated S-protein deposition needs further elucidation. [ABSTRACT FROM AUTHOR]

Two alternative integrins involved in mucosal homing (alpha 4 beta 7) or epithelial retention (alpha E beta 7) of lymphocytes were examined in the human gut. The distribution of the beta 7 subunit [monoclonal antibody (mAb) M301] was bimodal in that it was strongly expressed by alpha E beta 7 + cells but weakly by alpha 4 beta 7 + cells. More than 90% of intraepithelial lymphocytes (IEL), including the minor subsets of CD4+, T-cell receptor (TCR) gamma/delta +, and CD3- cells, expressed alpha E beta 7 as did most lamina propria CD8+ (88%) and a fraction (36%) of CD4+ lymphocytes. Conversely, B-lineage cells (CD19+) and macrophages (CD68+) were negative. In gut-associated lymphoid tissue (GALT: Peyer's patches and appendix) only a few (< 5%) cells were positive for alpha E beta 7 (confined to CD8+ lymphocytes and CD11c+ putative dendritic cells). A relatively small fraction of IEL (30-50%) expressed alpha 4 beta 7 (mAb Act-1), while most (70%) lamina propria T and B lymphocytes, blasts, plasma cells and macrophages were positive. In GALT, T lymphocytes expressed similar levels of alpha 4 beta 7 as in the lamina propria whereas relatively few B lymphocytes (< 50%) were positive. Isolated lamina propria CD8+, CD4+, CD19+, and CD38+ cells contained mRNA for alpha 4 and the former three subsets as well as appendix CD8+ cells also for beta 7 while only lamina propria CD8+ cells had mRNA for alpha E. Together, the results suggested that alpha E beta 7 and alpha 4 beta 7 are differentially regulated in inductive sites and effector sites of the human gut. Because lymphoid cells at both sites expressed mainly alpha 4 beta 7, this integrin may be a homing receptor on memory and effector cells bound for lamina propria as well as on naive lymphocytes extravasating in GALT. Conversely, because alpha E beta 7 was mainly expressed by CD8+ cells in epithelium and lamina propria, it was probably induced after extravasation, in agreement with the observation that IEL and a fraction of lamina propria T lymphocytes (mainly CD8+ cells) generally expressed higher levels of beta 7 than most CD4+ and B cells. Also a subset of putative dendritic cells located near the follicle-associated epithelium of GALT expressed alpha E beta 7, perhaps reflecting epithelial interaction during primary immune responses.

Expression of CD45RO on intraepithelial lymphocytes (IEL) bearing the T-cell receptor (TcR) alpha/beta or gamma/delta was studied in situ by three-colour immunofluorescence on jejunal tissue sections from 21 patients with coeliac disease and eight controls. CD45RA-TcR alpha/beta+ IEL expressed CD45RO significantly more often (75%) than the preferentially expanded TcR gamma/delta+ counterpart (59%). Triple staining for CD3, CD4/8 and CD45RA or CD45RB revealed that all CD3 + 4 - 8 - IEL (taken to be TcR gamma/delta+) expressed CD45RB and none were CD45RA. CD45RO positivity was of the same magnitude (66%) on the predominating monoclonal antibody delta TCS1-reactive fraction of TcR gamma/delta+ cells as on the remainder of the TcR gamma/delta+ subset. These results suggest that gluten exposition in patients with coeliac disease leads to accumulation of CD45RA-, putative antigen-primed memory cells of both TcR phenotypes. The less marked CD45RO expression within the preferentially expanded TcR gamma/delta+ subset of IEL may be of particular biological interest.