Nerve growth factor receptor expression on dendritic reticulum cells in follicular lymphoid proliferations

NGFR regulates stromal cell activation in germinal centers

Nerve growth factor receptor (NGFR) is expressed by follicular dendritic cells (FDCs). However, the role of NGFR in the humoral response is not well defined. Here, we study the effect of Ngfr loss on lymph node organization and function, demonstrating that Ngfr depletion leads to spontaneous germinal center (GC) formation and an expansion of the GC B cell compartment. In accordance with this effect, stromal cells are altered in Ngfr-/- mice with a higher frequency of FDCs, characterized by CD21/35, MAdCAM-1, and VCAM-1 overexpression. GCs are located ectopically in Ngfr-/- mice, with lost polarization together with impaired high-affinity antibody production and an increase in circulating autoantibodies. We observe higher levels of autoantibodies in Bcl2 Tg/Ngfr-/- mice, concomitant with a higher incidence of autoimmunity and lower overall survival. Our work shows that NGFR is involved in maintaining GC structure and function, participating in GC activation, antibody production, and immune tolerance.

Distribution of NGF receptors in normal and pathologic human lymphoid tissues

To identify nerve growth factor (NGF) target cells in normal and pathologic human lymphoid tissues, we have studied the expression of the low-affinity NGF receptor (p75LNGFR) and the high-affinity tropomyosin-related kinase NGF receptor (TrkA). A RNAse protection assay revealed the expression of trk transcripts in thymus, spleen, palatine tonsils and lymph nodes. TrkA immunoreactivity was shown in thymic epithelial cells, cryptic tonsillar epithelium and several monocyte-derived cells including epithelioid and multinucleated Langhans' cells, follicular dendritic cells and interdigitated reticular cells. TrkA immunoreactivity was rarely observed in normal T- and B-lymphocytes, but was intense in lymphoma cells of several B-cell lymphoma subtypes, anaplastic large cell lymphomas and Reed-Sternberg cells. Western blot analysis revealed the presence of p75LNGFR and of p80Trk and glycosylated Trk isoforms (gp110, gp140). p75LNGFR immunoreactivity was detected in epithelial Hassal's bodies, follicular dendritic cells, interdigitated reticular cells, periarteriolar macrophages, endothelial sinusal cells and nerve endings. The broad expression of NGF receptors may be an indicator of neurotrophin activity in lymphoid tissues and suggests their implication in inflammatory or lymphoproliferative disorders.

Acetyl cholinesterase is expressed in the follicular dendritic cells of germinal centres: differences between normal and neoplastic follicles

Acetyl cholinesterase (AcChE) was demonstrated by histochemistry in the follicular dendritic cells (FDCs) of the germinal centres of lymph nodes, tonsils, and bowel lymphoid tissue. Its presence in the FDCs was confirmed by double immunostaining for CD21 or DRC-1. AcChE-positive FDCs are concentrated in the inner portion of the light zone of the germinal centre, being absent from the dark zone. In the lymphoid tissue surrounding the germinal centres are AcChE-positive blood vessels; double staining shows that the AcChE is present in the pericytes surrounding the endothelium of the blood vessels. In contrast to the reactive follicle, the AcChE reactivity in FDCs of follicle centre lymphoma is absent or minimally expressed, although the dense FDC mesh is well stained with CD21 or DRC-1. This suggests that the AcChE is not constitutively expressed in FDCs but that its expression is influenced by the state and activity of the lymphoid cells in the germinal centre. The reduced level of AcChE staining can be profitably employed in the diagnosis of follicle centre lymphoma.

Expression of vascular cell adhesion molecule-1 in kidney allograft rejection

VCAM-1, a leukocyte adhesion molecule expressed by cytokine-activated endothelial cells in culture, may mediate mononuclear leukocyte infiltration in vessels and interstitium in solid organ allograft rejection. Using the avidin-biotin immunoperoxidase technique and an affinity-purified rabbit polyclonal antisera to recombinant human VCAM (rVCAM Ab) which works in methyl Carnoy's fixed tissues, we studied the expression of this molecule in biopsies of transplanted kidneys (N = 34) with and without features of rejection and allograft nephrectomies (N = 17) as well as nontransplanted control tissues (N = 26). The rVCAM Ab showed a population of reactive endothelial cells limited to sites of prominent subendothelial leukocytic cell infiltration in arteries and veins, and occasional peritubular capillaries (PTC) in rejecting allografts. Endothelial expression of VCAM was rarely identified in biopsies showing interstitial rejection only or cyclosporine toxicity, usually in PTC, and was only rarely encountered in nontransplanted control tissues. Apparent de novo expression of VCAM-1 by arterial smooth muscle cells and mesangial cells was present in cases of severe rejection. In addition, a population of cells (DC) with dendritic morphology was identified by rVCAM Ab within sites of lymphoid cell aggregation in rejecting allografts. Further evidence that these cells represent true DC was obtained by identification of VCAM-1 positive, morphologically similar cells in both germinal centers and interfollicular areas of all seven reactive lymph nodes tested; and by similar staining of these cells in the allografts and lymph nodes by antibodies to nerve growth factor receptor and the complement receptor CR1, previously shown to recognize DC. DCs were generally not seen in uninflamed normal control organs or portions of allografts uninvolved by lymphoid aggregates. Enhanced tubular epithelial cell expression of VCAM-1 was also present in rejecting allografts. All staining could be abolished by absorption of the antisera with VCAM-1 transfected, but not ICAM-1 or ELAM-1 transfected, CHO cells. In situ hybridization studies utilizing a cDNA probe to human VCAM-1 demonstrated mRNA production by glomerular, tubular and vascular cells corresponding to sites where the protein was immunohistochemically localized.(ABSTRACT TRUNCATED AT 400 WORDS)

Protection of germinal centres from complement attack: decay-accelerating factor (DAF) is a constitutive protein on follicular dendritic cells. A study in reactive and neoplastic follicles

The development of B-cell memory is linked to the presence of germinal centres. This process is dependent on the presence of antigen, usually in the form of immune complexes with antibody, on the surface of the follicular dendritic cells (FDCs) that form a network in the germinal centre. The presence of immune complexes poses a constant danger of activating complement. Decay accelerating factor (DAF, CD55) and the membrane attack complex (MAC) inhibitor (CD59) are two cell proteins whose sole function is to protect cells from the action of complement, the former affecting the earlier components of the complement cascade, and the latter the terminal ones; both are bound to the cell surface via a glycosylphosphatidylinositol link. DAF but not CD59 could be demonstrated on FDCs. DAF is also present on the FDCs in follicular lymphomas despite the absence of complement (C3) in neoplastic follicles. This indicates that DAF is constitutive to FDCs but does not preclude the possibility that its expression is increased when immune complexes are deposited.